gtk/imwayland: Use serial to control outbound messages

Following the text-input protocol changes at https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/115, use the serial number to have the client push changes to the zwp_text_input_v3 object only after compositor/client states match.

This specifically is more lenient to compositors pushing multiple .done events ahead of the client replying to them.

Closes: #3641 (closed)

Note: Marked as WIP until the protocol bits are resolved