Lazily create QMetaObjects

Lazily create QMetaObjects

For internal QML built types, creating a metaobject each time is
just wasteful.  Additionally, as the property caches were always
created from the intermediate QMetaObject, it was difficult to pass
information directly from the compiler to the property cache.

Change-Id: I769526b0edaaf16a86883f3065b75618b94e4077
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>