Adds light bulb helper which shows when a code action is available on the current cursor position.
The code actions are queried when the cursor is inside a word (non whitespace) and stays in the same position for more then 250ms. Code actions are not re-queried if the cursor stays inside the same word.
The added code should be straight forward to port to gtk4 (e.g. gtk_text_view_add_child_in_window -> gtk_text_view_add_overlay)