qtbase: a11y: Return correct string information for item views
This fixes the problem that NVDA spoke the accessible name of list views
and tree views two or three times.
The patch was backported/adjusted to Qt 6.7.
(cherry picked from commit 23531dd21027b4ddb81581f6096f6a865da641d8)
The patch was slightly adjusted to Qt 5.15.
- GnuPG-bug-id: T7854