Add dependency section to gdextension file docs

[paddy-exe]

Continuation of #9383
Fixes #9462

also removes a double word

[mhilbrunner]

Merged! Feedback by @dsnopek still appreciated, saw the review request too late, oops.

[paddy-exe]

@mhilbrunner No worries. I can patch it up very quickly if there is any feedback 👍🏻

[dsnopek]

This looks good to me!

The only note that I would add, is that the most common way to use [dependencies] is with a path of "", which means to copy the dependency into the same folder as the Godot executable, and so it'd be good to have an example of that, ie:

windows.debug = {
    "res://bin/libdependency.windows.template_debug.x86_64.dll" : "",
    "res://bin/libdependency.windows.template_debug.x86_32.dll" : ""
}

On MacOS, I think using the path "Contents/Resources" or "Content/Frameworks/" is common, but I'm not 100% sure about those.

In any case, I think we should try to include some paths that are actually used in the wild, in order to help folks figure out how to use this.

[YuriSizov]

Hey, @paddy-exe and @dsnopek! Am I missing something about these dependencies? When I looked into Godot codebase, I only saw OS_Android using this data. GDExtension::open_library takes the info and extracts paths from it, puts it into OS::GDExtensionData::library_dependencies, and then library_dependencies is only accessed in OS_Android::open_dynamic_library.

If this is only implemented on Android, then this must be reflected in the documentation in two ways: an explicit note and all examples for other platforms must be removed. Or am I missing some indirect use?

PS. Well, export plugins system also extracts this information for its own use via GDExtension::find_extension_dependencies, but that doesn't seem to be related to loading GDExtension libraries.

PPS. Or is that it, the export part is what handles most other platforms and that's sufficient? Sorry if this is a dumb question.

[paddy-exe]

@YuriSizov I haven't looked at the implementation for specific platforms but I assure you I have tested it both on Linux and even more extensively on Mac to make sure it works. I am not aware if there are more specific requirements for loading on mobile platforms though.

[mhilbrunner]

Cherry-picked to 4.2 in #9648.