GD-139: Enable addon script validation results in a lot of compile errors and warnings

[MikeSchulze]

The used GdUnit4 version:
latest master

The used Godot version:
v4.0.stable.official [92bee43ad]

OS including version:
Windows 10, MacOs

Describe the bug
Godot has exclude addons by default from the GdScript validation.

After remove the default flag i found a lot of compiler errors in the plugin

Steps to Reproduce

• include the addons to the GDScript validation see screenshot
• restart Godot

Check the errors:

--- Debug adapter server started ---
--- GDScript language server started ---
  res://addons/gdUnit4/src/core/GdUnitSingleton.gd:17 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  res://addons/gdUnit4/src/core/GdUnitSingleton.gd:20 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  res://addons/gdUnit4/src/core/GdUnitSingleton.gd:32 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  res://addons/gdUnit4/src/core/parse/GdDefaultValueDecoder.gd:0 - Parse Error: Could not resolve class "GdUnitSingleton".
  res://addons/gdUnit4/src/core/GdUnitMemoryPool.gd:0 - Parse Error: Could not resolve class "GdUnitSingleton".
  res://addons/gdUnit4/src/core/GdUnitMemoryPool.gd:30 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  res://addons/gdUnit4/src/core/GdUnitMemoryPool.gd:54 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  modules/gdscript/gdscript_compiler.cpp:2318 - Condition "!base->is_valid() && !base->reloading" is true. Returning: ERR_BUG
  modules/gdscript/gdscript_compiler.cpp:2318 - Condition "!base->is_valid() && !base->reloading" is true. Returning: ERR_BUG
  res://addons/gdUnit4/src/core/GdFunctionDoubler.gd:71 - Parse Error: The variable type is being inferred from a Variant value, so it will be typed as Variant. (Warning treated as error.)
  res://addons/gdUnit4/src/mocking/GdUnitMockFunctionDoubler.gd:0 - Parse Error: Could not resolve class "GdFunctionDoubler".
  modules/gdscript/gdscript_compiler.cpp:2318 - Condition "!base->is_valid() && !base->reloading" is true. Returning: ERR_BUG
  modules/gdscript/gdscript_compiler.cpp:2318 - Condition "!base->is_valid() && !base->reloading" is true. Returning: ERR_BUG
  res://addons/gdUnit4/src/network/rpc/RPCMessage.gd:14 - Parse Error: The method "to_string" overrides a method from native class "Object". This won't be called by the engine and may not work as expected. (Warning treated as error.)
  res://addons/gdUnit4/src/network/rpc/RPCGdUnitEvent.gd:14 - Parse Error: The method "to_string" overrides a method from native class "Object". This won't be called by the engine and may not work as expected. (Warning treated as error.)
  res://addons/gdUnit4/src/network/rpc/RPCGdUnitTestSuite.gd:14 - Parse Error: The method "to_string" overrides a method from native class "Object". This won't be called by the engine and may not work as expected. (Warning treated as error.)
Loading GdUnit4 Plugin success

Some of the errors i reported as Godot Bug.
74532

Minimal reproduction project: