This commit updates the screenshots for the Qt Widget examples. It also
removes several unused screenshots and adds several minor edits.
Task-number: QTBUG-69988
Change-Id: I23b90fd6c8b798169d158854609c09ef3f1c1a20
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit 618b1faf37ddda4cdeff6934f5af7e699c9aad63)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>