Clarify get_executable_path documentation for Mac

[AdamLearns]

This page of the documentation has the following blurb:

String get_executable_path ( ) const

Returns the path to the current engine executable.

Note: On macOS, always use create_instance instead of relying on executable path.

This makes it sound like it's wrong to ever use get_executable_path on macOS, but it's actually only if you're attempting to launch another instance of Godot that you should opt for create_instance. If you're instead doing something like trying to resolve res://, it seems like it's okay to use get_executable_path.

[Mickeon]

In #80282 this line went unchanged due to severe lack of context, so I heavily appreciate this. Wording matches that prior PR, too.

The prior line was written by by @bruvzg 3 years ago.

[Mickeon]

Would be nice if both the commit and the title of this PR were more self-explanatory, by the way.

[AdamLearns]

Would be nice if both the commit and the title of this PR were more self-explanatory, by the way.

I've updated both. 👍

[bruvzg]

If you're instead doing something like trying to resolve res://, it seems like it's okay to use get_executable_path.

That's bad example, you should use ProjectSettings.globalize_path(path) to resolve res:// and similar path. But in general, get_executable_path is good to use if you want an executable path (or path of something relative to executable).

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉