cmd/compile: constant-fold loads from constant dictionaries and types

cmd/compile: constant-fold loads from constant dictionaries and types

Update #59591

Change-Id: Id250a7779c5b53776fff73f3e678fec54d92a8e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/486895
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>