Fix file disappearing when renaming dependencies

[KoBeWi]

Fixes #86174

When renaming a file, the editor will try to fix dependencies, but it will save affected scenes before that. However as a result of saving, the dependency might get removed thus a rename is performed on a dependency that no longer exists.

Then there is rename method that creates a .depren file after renaming dependency. However it treats "no rename" as success

godot/scene/resources/resource_format_text.cpp

Lines 921 to 924 in f8a2a91

	//nothing was done
	if (fw.is_null()) {
	return OK;
	}

meaning the file is not created, but the code continues normally. This results in a disaster.

The fix checks whether .depren file actually exists before removing the old file. Another option would be making the rename method return an error if the dependency can't be found, but I'm not sure if it's always expected to exist (in case of the fixed issue it didn't, but maybe it's expected to fail, idk).
I modified the binary format too, but I didn't test if the same bug occurs. Better to be safe anyway.

This was probably regression from #81725 or #81657

[adamscott]

@YuriSizov This should be a patch for 4.2.2

[Jordyfel]

Since saving scenes can change dependencies, what do you think about swapping these calls:
Impossible, my bad.

godot/editor/filesystem_dock.cpp

Lines 2004 to 2009 in f8a2a91

	// Look for files that use these moved/renamed resource files.
	_find_file_owners(EditorFileSystem::get_singleton()->get_filesystem(), renamed_files, r_file_owners);
	// Open scenes with dependencies on the ones about to be moved will be reloaded,
	// so save them first to prevent losing unsaved changes.
	EditorNode::get_singleton()->save_scene_list(r_file_owners);

[KoBeWi]

save_scene_list() uses r_file_owners(), which is filled by _find_file_owners(), so they can't be swapped. Maybe an alternative is simply saving every scene, but changing behavior would require more testing. The current solution is a safer option.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.2.2.