[dev.typeparams] all: merge dev.regabi (cb05a0aa) into dev.typeparams

Merge List:

+ 2021-01-05 cb05a0aa [dev.regabi] cmd/compile: remove toolstash scaffolding
+ 2021-01-05 98218388 [dev.regabi] cmd/compile: remove CaptureVars
+ 2021-01-05 fd43831f [dev.regabi] cmd/compile: reimplement capture analysis
+ 2021-01-05 fb69c67c [dev.regabi] test: enable finalizer tests on !amd64
+ 2021-01-05 81f4f0e9 [dev.regabi] cmd/compile: remove race-y check in Name.Canonical
+ 2021-01-05 4a9d9ade [dev.regabi] cmd/compile: remove initname function

Change-Id: I519f349ff62b6c9bc5db2a0d34feef4b5d42cbae