Re-enable NonMovingAlloc operations in ThreadStress, except with GSS.

When the Generational Semi-Space (GSS) collector is used,
explicitly assign frequencies to all ThreadStress operations
and set the frequency of NonMovingAlloc operations to 0.

Also properly handle ThreadStress' `-nonmovingalloc` option,
which was documented but not implemented.

Test: art/test/testrunner/testrunner.py -t 004-ThreadStress (with GSS)
Test: art/test/testrunner/testrunner.py -t 004-ThreadStress (without GSS)
Bug: 72738921
Change-Id: Ia033a77d997eafa2bfa7244697ba7ffe31926133