cmd/compile: preserve/translate names for parameters

This is part of getting debugging into good shape
with the register ABI.  (This may generate a backport
for 1.16, there was some regression there as well.)

This is not necessarily fully-baked yet; my goal is to
make it work "well enough" for actual debugging, then
revisit the metrics, which are currently ignorant
of registers used for passing parameters (currently,
rejects them as a valid option).

Updates #40724.

Change-Id: Ib649adf39f947b7b54895c5bf181cf48ca4d38a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/311689


Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>