Add support to moc for registering non-local enums via Q_ENUMS.

Add support to moc for registering non-local enums via Q_ENUMS.

When using the Q_ENUMS macro to register an enumeration in a class
with moc, it's now possible to provide a scoped enumeration that
exists in another class. This adds the enum class scope to
a metaobject's list of related classes stored in the extradata
field.

This allows the declarative code to handle non-local enums in
signal and slot functions that are exposed to QML.

Task-number: QTBUG-20639
Change-Id: I94f5292818095fda75762bd1508ba5c69de19503
Reviewed-by: Martin Jones <martin.jones@nokia.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>