compiler: change escape maps to hash tables

Also use just one table lookup, not two.

Change-Id: Iddebaabb7d276f65e70b021035071bfc7c8a75ec
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/197759
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2 files changed