Integration with GDScript

[dogboydog]

Several users have expressed an interest in primarily using GDScript in their projects using YarnSpinner-Godot

Goals:

• Provide examples for interactions that already work out of the box, such accessing methods and fields on the DialogueRunner.
• Support creation of custom views via GDScript, by providing a C# adapter class which forwards the method calls from DialogueViewBase methods to your GDScript node instance.
• Similarly, support creation of custom variable storage via GDScript.
• Reasonably match conventions for GDScript related APIs
• Provide the ability to register commands and functions purely via GDScript (I found this is possible using a combination of get_method_list and a Callable for the command handler, but it has some complications that have to be smoothed out)
• Make sure that some version of VariableStorage TryGetValue is callable from GDScript, test the other functionality of variable storage as well

Challenges:

• In some testing, I found that when passing a LocalizedLine from C# to GDScript, MarkupParseResult fields such as TextWithoutCharacterName were inaccessible. The C# view adapter should likely convert LocalizedLine to an object that will be more readily consumed from GDScript, such as a Dictionary with a set of known keys.

It's worth noting that these changes will still require the user to install the version of the engine that supports C# - it will just reduce the amount that you have to use C# in order to use the plugin.