Provide the new comparesEqual() helper function as an implementation of
the (in)equality operators and compareThreeWay() helper function for
the rest of the relational operators.
Use Q_DECLARE_STRONGLY_ORDERED to provide all relational operators.
Use the new Qt::totally_ordered_wrapper to wrap the "d" pointer to
avoid UB when performing comparisons of QExplicitlySharedDataPointer.
Add some comparisons related tests for QExplicitlySharedDataPointer.
Use QT_TEST_ALL_COMPARISON_OPS macros in unit-tests.
Task-number: QTBUG-120306
Change-Id: I275484a96a57da2df92712ac97e237a88a889da5
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
793f3d8642