[AArch64] Make stack tagging compatible with SLH

See https://github.com/llvm/llvm-project/issues/61830

Speculative Load Hardening (SLH) requires that conditional branches are
implemented using B.cc branches, not using {TC}B{N}Z branches.

Stack tagging was expanding one of the pseudo instructions it uses to
cbnz. This commit changes that to use b.ne instead.

Note that the added regression test was added to settag.ll rather than
speculation-hardening.ll. The speculation-hardening.ll tests also check
that all tests in the file work with global-isel. It seems that stack
tagging does not work yet with global-isel. Therefore, testing the
combination of stack tagging and SLH hard to be added to a test file
that doesn't test global-isel, i.e. settag.ll

Differential Revision: https://reviews.llvm.org/D148508