Closes https://github.com/godotengine/godot-proposals/issues/2721
On `EditorFileDialog`:
* Add filter box that only shows folders and files in current directory that match
* Add sort button to sort files and directories
* Add a shortcut for CTRL+F for selecting the filter box
Also moved common code between `EditorFileDialog` and `FileSystemDock`
to it's own file.
Co-authored-by: fox <12120644+foxydevloper@users.noreply.github.com>
