Suggest using OS.has_feature instead of the engine architecture name for bitness

[aaronfranke]

I was reading this proposal godotengine/godot-proposals#11150 and checking our own docs when I realized that the documentation for Engine.get_architecture_name is sub-optimal. Users should not be trying to heuristically extract information from the architecture name. If users need to answer boolean questions about the platform, they should use OS.has_feature which returns a boolean depending on various feature flags.

[Mickeon]

I agree this tip has always been oddly unreliable, as if it was written before Feature Tags were even a thing.

[fire]

The pull request makes sense to update the documentation to use an existing feature rather than extract it from the architecture name.