[AArch64][PAC] Rework discriminator analysis for calls and tail calls
Make use of fixupBlendComponents for AUTH_TCRETURN[_BTI] and for
BLRA[_RVMARKER] pseudos the same way it is done for AUT/PAC/AUTPAC.
This patch unifies discriminator analysis for DAGISel and GlobalISel
and improves cross-BB analysis in case of DAGISel.