GDExtension: Ensure that we have automated build CI for Windows and MacOS

This was originally reported by @NicholasBolen in #351:

Unrelated, but Is the standalone version only for linux? I get various errors after installing.

ERROR: core/extension/gdextension_library_loader.cpp:369 - No GDExtension library found for current OS and architecture (windows.x86_64) in configuration file: res://addons/addons/GDQuest_GDScript_formatter_standalone/bin/gdscript_formatter.gdextension
ERROR: GDExtension dynamic library not found: 'res://addons/addons/GDQuest_GDScript_formatter_standalone/bin/gdscript_formatter.gdextension'.
ERROR: res://addons/addons/GDQuest_GDScript_formatter_standalone/plugin.gd:481 - Parse Error: Identifier "GDScriptFormatter" not declared in the current scope.
ERROR: res://addons/addons/GDQuest_GDScript_formatter_standalone/plugin.gd:496 - Parse Error: Identifier "GDScriptFormatter" not declared in the current scope.

@khellste, could you take a look at this?

I'm opening this as a separate issue since it appears to be unrelated to the packaging issue in #351.

Commencez par examiner les erreurs de chargement de GDExtension dans core/extension/gdextension_library_loader.cpp ainsi que le point d’entrée du plugin autonome dans plugin.gd, puis inspectez la configuration CI de build existante. La tâche est considérée comme terminée lorsque les builds automatisés pour Windows et macOS produisent des bibliothèques GDExtension que le plugin autonome peut charger sur ces plateformes.