Crash when creating QWindow

See QTBUG-58107. It seems the init() function that recreates a QWindow for each test triggers a regression somewhere in the cocoa qpa. The linked commit temporarily works around this by using initTestCase() instead of init().

Use the state of qt3d prior to the fix for QTBUG-58107 to git bisect qtbase. The previous version of qtbase that is thought to be OK is 8266de089cdc85a5ac93361e22722ba817878c4b but this needs to be compared with when these graphics helper tests were introduced.

Once issue in qtbase is solved, we should revert https://codereview.qt-project.org/#/c/182144/.