Always emit reset for IM preedit with mouse click

Hangul inputs treat pre-edit text as output text and the pre-edit
text won't be moved with mouse click.
Now the reset signal is always emitted simply with mouse click and
each IM engine could handle the signal whether the preedit is committed,
cleared or kept.

Closes #1534
4 jobs for reset-with-click in 17 minutes and 28 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #221679
fedora-x86_64

00:06:05

passed #221680
win32
msys2-mingw32

00:10:31

 
  Flatpak
passed #221681
flatpak:demo

00:06:57

passed #221682
flatpak:widget-factory

00:06:27