Expose EditorFileSystemDirectory.get_file_resource_script_class() to scripting

[Okxa]

Describe the project you are working on

Plugin which interacts with resource files in a project.

Describe the problem or limitation you are having in your project

There is no way to get class_name of a Resource with EditorFileSystemDirectory nor EditorFileSystem

(Sidenote; there is a way to get the type, but that is not the class_name:
https://docs.godotengine.org/en/stable/classes/class_editorfilesystem.html#class-editorfilesystem-method-get-file-type
https://docs.godotengine.org/en/latest/classes/class_editorfilesystemdirectory.html#class-editorfilesystemdirectory-method-get-file-type)

Describe the feature / enhancement and how it helps to overcome the problem or limitation

The FileInfo struct appears to have the desired information, according to the comment:

	struct FileInfo {
		String file;
		StringName type;
		StringName resource_script_class; // If any resource has script with a global class name, its found here.

https://github.com/godotengine/godot/blob/f952bfe9985ad8f507cc29b2c7601bbba18b8039/editor/editor_file_system.h#L59

However, there is no way to get this information in editor scripts.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Exposing the function get_file_resource_script_class() from EditorFileSystemDirectory to scripting would solve this:

StringName EditorFileSystemDirectory::get_file_resource_script_class(int p_idx) const {
	ERR_FAIL_INDEX_V(p_idx, files.size(), "");
	return files[p_idx]->resource_script_class;
}

https://github.com/godotengine/godot/blob/f952bfe9985ad8f507cc29b2c7601bbba18b8039/editor/editor_file_system.cpp#L189-L192

Also note that EditorFileSystem itself has a convience function to get the type of a file, (which internally uses EditorFileSystemDirectory):

String EditorFileSystem::get_file_type(const String &p_file) const {
	EditorFileSystemDirectory *fs = nullptr;
	int cpos = -1;

	if (!_find_file(p_file, &fs, cpos)) {
		return "";
	}

	return fs->files[cpos]->type;
}

https://github.com/godotengine/godot/blob/f952bfe9985ad8f507cc29b2c7601bbba18b8039/editor/editor_file_system.cpp#L1855-L1864

So it might be a good idea to also do that for this one, although that is left up to debate.

If this enhancement will not be used often, can it be worked around with a few lines of script?

Only by loading the resource and checking for type, or reading the first line of a non-binary resource and manually checking for the script_class text.

Is there a reason why this should be core and not an add-on in the asset library?

Editor functionality.