QTextDocument: fix an off-by-one in the changed signal for lists

When blocks are added or removed in block groups, i.e. items added or
removed from text lists, the whole group is marked as changed, but the
calculation of the before/after group length would be one off. That
was reflected in the contentsChange signal.

Add unit test. Since the whole group changes when list items are
added, text is removed and the change-begin is not where the cursor
was when the change was made.

Fixes: QTBUG-82455
Pick-to: 6.2 5.15
Change-Id: I99ee2cfef4944fcac8aca492741fd0f3b0de4920
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

0 files changed, 0 insertions, 0 deletions