Cleanup mess in public type ids.

Cleanup mess in public type ids.

There is no reason to keep two separated core types sets. It
couldn't be fixed before Qt5 because of binary compatibility promise.

This patch merges QMetaType core types with ext core types.

This "simple" operation consists of:
- QDataStream version was incremented, because type ids are
saved in QVariant's data stream.
- QMetaType LastExtCoreType and FirstExtCoreType were replaced by
LastCoreType, FirstCoreType and new QMetaType::HighestInternalId.
- New tests checking QVariant data stream for Qt4 and for Qt5 versions
were added.

Change-Id: I02dd74d29317365c297a789a4eb7c9c5edc3b231
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>