text-input: update to 3.2

Here's an attempt to move text_input_v3 forward without a full v4/text-input-next bump. I have gathered the hopefully least controversial or most backwards compatible bits:

• "No emoji" hint (!136)
• IM caret + surface synchronization (!72)
• An action system (!73)
• A "preedit shown" hint (!66)
• A solution for type-to-search, where IMs may miss the key event(s) popping up the entry (!233)

Left out:

• !234, needs buy-in by IM authors (and possibly input_method protocol changes), or it will be a well-intentioned but useless api.
• !71, this second commit mode can be shortcut at the compositor level without exposing to clients. It is what Mutter/GNOME Shell did.
• Other more fundamental changes, these feel like should be pondered/addressed in a distinct version
  • Explicit reset mode, !34
  • Chars vs. offsets
  • Meaning/management of serials

Implementations:

• Mutter (https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3600)
• GTK (https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/6922)
• TBD
• TBD

Acks:

• TBD
• TBD
• TBD