[dev.regabi] cmd/compile: rename CommStmt and CaseStmt [generated]

Rename these two AST nodes to match their cmd/compile/internal/syntax
and go/ast counterparts.

Passes toolstash -cmp.

[git-generate]
cd src/cmd/compile/internal/ir
rf '
	mv CaseStmt CaseClause
	mv CommStmt CommClause
'
sed -E -i -e 's/(Case|Comm)Stmt/\1Clause/g' mknode.go

Change-Id: I19fba0323a5de1e71346622857011b2f7879bcef
Reviewed-on: https://go-review.googlesource.com/c/go/+/280446


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>