Fix cursor position adjustment when removing strings

Fix cursor position adjustment when removing strings

Commit 0ba1b4d0 introduced a regression to QTextDocument: it postponed
cursor position adjustment until the move operation is done, but
contentsChanged will be triggered by finishEdit() in this move
operation, thus cursor positions in this signal handler will be in
inconsistent states (normally we should first update cursor position
then trigger contentsChanged). In this case we should also postpone
finishEdit() handling after cursor positions have been adjusted, then
the states expose to applications will be consistent.

Task-number: QTBUG-15857
Reviewed-by: Eskil
(cherry picked from commit 34c297faca93e1286573b2a01127e4e7af00aff2)