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

[DevTwilight]

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.

[NathanLovato]

We don't have a build of the gdextension for all platforms just yet. I can take care of it sometime (unless someone wants to tackle this)

[khellste]

@NathanLovato beat me to the reply. The fix here is to distribute the new gdextension .dll and .so files with the new standalone addon. Apologies for the weird state that the standalone addon is in.

@DevTwilight - in the mean you can build it yourself with cargo build and copy the built DLL into the indicated folder.

[DevTwilight]

i am not using the addon it was @NicholasBolen