JIT: Avoid xchg for resolution (#81216)

JIT: Avoid xchg for resolution (#81216)

LSRA today uses xchg for reg-reg resolution when there are cycles in the
resolution graph. Benchmarks show that xchg is handled much less
efficiently by Intel CPUs than using a few movs with a temporary
register. This PR enables using temporary registers for this kind of
resolution on xarch (it was already enabled for non-xarch
architectures). xchg is still used on xarch if no temporary register is
available.

Additionally this PR adds support for getting a temporary register even
for shared critical edges. Before this change we would spill on
non-xarch for this case.

Finally, we now try to prefer a non callee saved temporary register so
that we don't need to save/restore it in prolog/epilog.

This mostly fixes the string hashcode regressions from #80743.