In some IM backends pre-edit text should be submitted on user interaction, in some it should be discarded.
In TextInputV1 and V2 this was a flag sent to the client along with
the commit string ahead of time.
TextInputV3 does not have a flag for this, so we handle it compositor side.
We flush the text to be committed :
- when we change keyboard focus, before the current client gets wl_keyboard.leave
- when a mouse is pressed in the relevant surface
- when a key is pressed and the InputMethod doesn't have a grab
- when the InputMethod forwards a key to the client
(which includes the InputMethod passing on grabbed keys)
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