Improve the project manager UI

This incorporates many suggestions from #31342.

This also revises the search behavior to be simpler and more efficient:

- Searching will now search in both the project name and path. A project
  will be displayed if either of these match the search term.
- If the search term contains a "/", the whole path will be used to match
  the search term. Otherwise, only the last path component will be used.

editor/project_manager.h

@@ -152,6 +152,7 @@ protected:
 
 public:
 	void _setup_filters(Vector<String> options);
+	void add_filter_option();
 	void add_search_box();
 	void set_filter_size(int h_size);
 	String get_search_term();