Handle QQmlPropertyData::DontRemoveBinding flag with new-style bindings

The QML engine has the concept of writes which leave existing bindings intact. This is done by passing QQmlPropertyData::DontRemoveBinding to the various QQmlPropertyPrivate::write* functions.

This functionality seems to be primarily used in the Animation system;
tst_qquickbehaviors replaceBinding fails if this is not supported even with the WIP implementation of interception for Behavior.