Add QU8SV vs QSV, QU8SV vs QChar, and QU8SV vs char16_t relational
operators.
This allows to get rid of the dummy relational operators in
tst_qstringapisymmetry.
Task-number: QTBUG-117661
Change-Id: If95d7418efd13c505ed0e3bef748b86ff55e623a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>