Fix issues related to code-signing for macOS exports

[mihe]

This PR fixes the following issues related to code-signing macOS exports:

1. When exporting projects that reference a GDExtension bundled as a *.framework, you will currently see error messages about MachO: Can't open file: [...] due to certain places in EditorExportPlatformMacOS assuming that all extensions are files, whereas *.framework is a directory.
2. When using Godot's built-in code-signing for macOS (on Windows in my case) for a project that references a GDExtension bundled as a *.framework, you will currently end up with a bunch of errors about LipO: Can't open file: [...] due to Godot thinking that the Resources directory is a bundle directory. This seemed to be the result of the regular expressions in _codesign_file not accounting for the slash at the end being optional for the Resources directory.
3. Godot's built-in code-signing does not seem to support the *.framework bundle layout with which I distribute Godot Jolt currently, where I don't have a Versions directory (since I can't reasonably distribute symlinks) but instead just the binary and a Resources directory at the top-level. While this layout probably raises some eyebrows, it works just fine with regular codesign as well as notarytool, so I don't see why Godot shouldn't support it too.

CC @bruvzg

[akien-mga]

Thanks!