[HotColdSplit] Reflect full cost of parameters in split penalty

[HotColdSplit] Reflect full cost of parameters in split penalty

Make the penalty for splitting a region more accurately reflect the cost
of materializing all of the inputs/outputs to/from the region.

This almost entirely eliminates code growth within functions which
undergo splitting in key internal frameworks, and reduces the size of
those frameworks between 2.6% to 3%.

rdar://49167240

Patch by: Vedant Kumar(@vsk)
Reviewers: hiraditya,rjf,t.p.northover
Reviewed By: hiraditya,rjf

Differential Revision: https://reviews.llvm.org/D59715