[Compiler] Support optional chaining in compiler

[SupunS]

Work towards #3976

Description

Performs a nil check on the target/parent before accessing a field or a method. If the target/parent is not nil, then unwraps the value and proceed to access the field or invoke a method on it. Otherwise, if the target/parent is nil, simply load a nil value onto the stack.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:feature/compiler commit 98d3f17
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -benchmem -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Collapsed results for better readability

[turbolent]

Great work! 👏