GD-707: Replace deprecated functions

[MikeSchulze]

Describe What
GdUnit4 uses deprecated functions, and we should replace it by suggested functions.

Describe Why
A user reports script errors when building Godot without deprecated functions, and we should replace them sooner rather than later.

• inst_to_dict
• dict_to_inst
• convert

Dev hints

Loading GdUnit4 Plugin success
  ERROR: res://addons/gdUnit4/src/core/GdUnitRunnerConfig.gd:66 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitRunnerConfig.gd:103 - Parse Error: Function "dict_to_inst()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Cannot infer the type of "d" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Cannot infer the type of "clazz_info" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/doubler/GdFunctionDoubler.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Cannot infer the type of "d" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Cannot infer the type of "clazz_info" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/doubler/CallableDoubler.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Cannot infer the type of "d" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Cannot infer the type of "clazz_info" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/doubler/GdUnitClassDoubler.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/execution/stages/GdUnitTestSuiteAfterStage.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:163 - Parse Error: Cannot infer the type of "d" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdObjects.gd:555 - Parse Error: Cannot infer the type of "clazz_info" variable because the value doesn't have a set type.
  ERROR: res://addons/gdUnit4/src/core/parse/GdUnitExpressionRunner.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/execution/stages/fuzzed/GdUnitTestCaseFuzzedTestStage.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/execution/stages/fuzzed/GdUnitTestCaseFuzzedExecutionStage.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/execution/stages/GdUnitTestCaseExecutionStage.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/execution/stages/GdUnitTestSuiteExecutionStage.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:170 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:180 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:182 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/execution/GdUnitTestSuiteExecutor.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/runners/GdUnitBaseTestRunner.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/network/rpc/RPC.gd:13 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/network/rpc/RPC.gd:17 - Parse Error: Function "dict_to_inst()" not found in base self.
  ERROR: res://addons/gdUnit4/src/network/rpc/RPC.gd:21 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/network/rpc/RPC.gd:37 - Parse Error: Function "dict_to_inst()" not found in base self.
  ERROR: res://addons/gdUnit4/src/network/rpc/RPCClientConnect.gd:2 - Parse Error: Could not resolve class "RPC".
  ERROR: res://addons/gdUnit4/src/network/GdUnitTcpClient.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/runners/GdUnitTestRunner.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: modules/gdscript/gdscript.cpp:3022 - Failed to load script "res://addons/gdUnit4/src/core/runners/GdUnitTestRunner.gd" with error "Parse error".
  ERROR: res://addons/gdUnit4/src/core/writers/GdUnitCSIMessageWriter.gd:112 - Parse Error: Function "Color8()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/writers/GdUnitCSIMessageWriter.gd:121 - Parse Error: Function "Color8()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitRunnerConfig.gd:66 - Parse Error: Function "inst_to_dict()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitRunnerConfig.gd:103 - Parse Error: Function "dict_to_inst()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:170 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:180 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/GdUnitTestSuiteScanner.gd:182 - Parse Error: Function "convert()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/runners/GdUnitTestCIRunner.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/bin/GdUnitCmdTool.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/src/core/writers/GdUnitCSIMessageWriter.gd:112 - Parse Error: Function "Color8()" not found in base self.
  ERROR: res://addons/gdUnit4/src/core/writers/GdUnitCSIMessageWriter.gd:121 - Parse Error: Function "Color8()" not found in base self.
  ERROR: res://addons/gdUnit4/bin/GdUnitCopyLog.gd:0 - Compile Error: Failed to compile depended scripts.
  ERROR: res://addons/gdUnit4/test/cmd/runtestDebug.tscn::GDScript_54n73:0 - Compile Error: Failed to compile depended scripts.
  WARNING: core/io/resource_format_binary.cpp:1094 - 'res://addons/gdUnit4/test/core/resources/scenes/simple_scene.scn': In external resource #1, invalid UID: 'uid://mdg54o4ynxsl' - using text path instead: 'res://addons/gdUnit4/test/core/resources/scenes/icon.png'.
  WARNING: scene/resources/resource_format_text.cpp:447 - res://addons/gdUnit4/test/core/resources/scenes/simple_scene.tscn:4 - ext_resource, invalid UID: uid://mdg54o4ynxsl - using text path instead: res://addons/gdUnit4/test/core/resources/scenes/icon.png