[dev.typeparams] cmd/compile: skip escape analysis diagnostics for wrappers

This CL changes escape analysis to skip reporting diagnostics (at
least for parameter tagging) for generated wrappers.

We're inconsistent about when/where wrappers are generated, which made
errorcheck tests of escape analysis unnecessarily brittle to changes
in wrapper generation. This CL addresses this making errorcheck tests
only care about tagging of the actual functions themselves, not the
wrappers too.

Change-Id: Ia1a0b9dabee4d4162b05647f871db03b032c945a
Reviewed-on: https://go-review.googlesource.com/c/go/+/330689


Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>