QPair: specialise QTypeInfo based on the typeinfos of its arguments

QPair: specialise QTypeInfo based on the typeinfos of its arguments

Specialise QTypeInfo<QPair<T1,T2>> based on the properties of
T1 and T2:

- If either T1 or T2 is Q_COMPLEX_TYPE, so is QPair<T1,T2>.
- Otherwise, if either T1 or T2 is Q_MOVABLE_TYPE, so is QPair<T1,T2>.
- Otherwise, QPair<T1,T2> is Q_PRIMITIVE_TYPE.

Change-Id: I8aecbd37e3b7924f77f38967498deabf1a19ca24
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>