Improve qFloatDistance() test coverage

Four code-paths that weren't tested are simply those with the
parameters swapped from code-paths we did test.  In any case, the
float-distance between values should be symmetric, so test that.

Task-number: QTBUG-88183
Change-Id: I2060eb77b1abada5b0fd5f4557dbb1761c5cfd02
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/global/qnumeric/tst_qnumeric.cpp

@@ -370,6 +370,7 @@ void tst_QNumeric::distance()
     QEXPECT_FAIL("denormal", "See QTBUG-37094", Continue);
 #endif
     QCOMPARE(qFloatDistance(from, stop), expectedDistance);
+    QCOMPARE(qFloatDistance(stop, from), expectedDistance);
 }
 
 // Whole number tests: