Restrict v8 property lookup to the execution context

Restrict v8 property lookup to the execution context

When resolving property names, only properties known to the current
context of execution should be available.  If a property name has
been overriden by a component extension, code executing in the
context of the base component should resolve the property name to
the property available inside the base component or its bases.

Task-number: QTBUG-24891
Change-Id: I9687cc28e108226d5a939627a901c8254344b598
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>
Reviewed-by: Martin Jones <martin.jones@nokia.com>