Make a copy of cmd/internal/edit for use in this repo.
This copy is taken from rsc.io/edit which is the cleaned up
external version of cmd/internal/edit. (We don't want
an rsc.io dependency in golang.org/x either.)
Change-Id: I9d8ed5d58f61f14e032c613af711fafa050c7f3e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/513736
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Russ Cox