[AArch64][GlobalISel] Fold G_AND into G_BRCOND

When the G_BRCOND is fed by a eq or ne G_ICMP, it may be possible to fold a
G_AND into the branch by producing a tbnz/tbz instead.

This happens when

  1. We have a ne/eq G_ICMP feeding into the G_BRCOND
  2. The G_ICMP is a comparison against 0
  3. One of the operands of the G_AND is a power of 2 constant

This is very similar to the code in AArch64TargetLowering::LowerBR_CC.

Add opt-and-tbnz-tbz to test this.

Differential Revision: https://reviews.llvm.org/D73573