Rather than replacing the whole file on gofmt or goimports, use the Myers
diff algorithm to compute diffs for a file. We send those back as text
edits.
Change-Id: I4f8cce5b27d51eae1911049ea002558a84cdf1bf
Reviewed-on: https://go-review.googlesource.com/c/158579
Reviewed-by: Ian Cottrell <iancottrell@google.com>
