Fix isQtQuickControl check with Qt 5.7
Review Request #127524 - Created March 29, 2016 and submitted
Only check for QQuickItem instead of private class names.
Also changed remaining places to use the isQtQuickControl function.
Works fine with Qt 5.7
I think we should not test for className().startsWith("QQuickStyleItem") because there is a new QtQuickControls2 module that could have QQuickStyleItem2 class (does not currently).
hmmm. This doubles the overhead ... and since this is called more and more often to differenciate normal widgets from qqc, this might become not so negligible.
(not to mention that this whole thing is not very satisfactory coming from upstream. not your fault).
anyway: shouldn't we make ugly ifdefs instead to ask the right class name for the right version ?
Will make code ugly, but it is already anyway;