[AArch64][PAC] Support BLRA* instructions in SLS Hardening pass

Make SLS Hardening pass handle BLRA* instructions the same way it
handles BLR. The thunk names have the form

    __llvm_slsblr_thunk_xN            for BLR thunks
    __llvm_slsblr_thunk_(aaz|abz)_xN  for BLRAAZ and BLRABZ thunks
    __llvm_slsblr_thunk_(aa|ab)_xN_xM for BLRAA and BLRAB thunks

Now there are about 1800 possible thunk names, so do not rely on linear
thunk function's name lookup and parse the name instead.

Author: atrosinenko