Adapt QToolButton texts to descriptive versions.
Add dummy stylesheet that will be used for all test functions, and a
specific style sheet to test rendering of QToolButton with a menu button.
Task-number: QTBUG-100401
Pick-to: 6.3 6.2
Change-Id: I5440407ddb3ea5b45124e77a6f0d1013362b4398
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>