Behavior should not trigger when the tracked value has not changed.

Behaviors are specifically for animating changes in value. When the
value has not changed, do not trigger the animation. This ensures
the animation system is not unnecessarily woken.

[ChangeLog][QtQuick][Behavior] Do not trigger a Behavior when the
tracked value has not changed.

Task-number: QTBUG-21549
Change-Id: I5b20121ccfb75ea5ebf86705df89891c94cf6e7e
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
QQmlMetaType: adapt to upcoming MOC format change

A change is pending on qtbase that turns relatedMetaObjects into a
const pointer-to-const in order to make the relocation a read-only
one.

Adapt.

Change-Id: I503eca13c1fe80d070e3078620fa3fd5ecdef0b0
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>