[MachineSink][AArch64] Sink instruction copies when they can replace copy into...

[MachineSink][AArch64] Sink instruction copies when they can replace copy into hard register or folded into addressing mode

This patch adds a new code transformation to the `MachineSink` pass,
that tries to sink copies of an instruction, when the copies can be folded
into the addressing modes of load/store instructions, or
replace another instruction (currently, copies into a hard register).

The criteria for performing the transformation is that:
* the register pressure at the sink destination block must not
  exceed the register pressure limits
* the latency and throughput of the load/store or the copy must not deteriorate
* the original instruction must be deleted

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D152828