Avoid early IM reset on updates
Resetting the IM on IM updates is too eager and indeed the simple IM context doesn't like that this happens in the middle of dead key handling.
We however want to reset the IM after actual text buffer changes (say, a committed string) moved the cursor position, altered the surrounding text, etc. So that the IM implementation does know to update its state.
Fixes: 9e29739e ("gtktext: Shuffle the places doing IM reset") Closes: #5133 (closed)