Allow literal enum to int property assignments

Allow literal enum to int property assignments

Previously, enum to int property assignments were considered bindings.
This commit adds support for assigning enum values to int properties
as enums.

Note that to use an enum in QML, it must have been declared with
Q_ENUMS or otherwise registered as a metatype.  Enum values from the
global Qt object are also usable.

Task-number: QTBUG-23403
Change-Id: I50db6cae54a24400ea472bde43619d547e4ceb78
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>