[dev.regabi] cmd/compile: first pass at abstracting Type

[dev.regabi] cmd/compile: first pass at abstracting Type

Passes toolstash/buildall.

[git-generate]
cd src/cmd/compile/internal/ssa
rf '
ex . ../ir ../gc {
  import "cmd/compile/internal/types"
  var t *types.Type
  t.Etype -> t.Kind()
  t.Sym -> t.GetSym()
  t.Orig -> t.Underlying()
}
'

cd ../types
rf '
mv EType Kind
mv IRNode Object

mv Type.Etype Type.kind
mv Type.Sym Type.sym
mv Type.Orig Type.underlying
mv Type.Cache Type.cache

mv Type.GetSym Type.Sym

mv Bytetype ByteType
mv Runetype RuneType
mv Errortype ErrorType
'

cd ../gc
sed -i 's/Bytetype/ByteType/; s/Runetype/RuneType/' mkbuiltin.go

git codereview gofmt
go install cmd/compile/internal/...
go test cmd/compile -u || go test cmd/compile

Change-Id: Ibecb2d7100d3318a49238eb4a78d70acb49eedca
Reviewed-on: https://go-review.googlesource.com/c/go/+/274437
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>