internal/lsp: clean up ApplyEdits
internal/lsp: clean up ApplyEdits

This should be a faster but equivalent implementation.

Change-Id: I7bc756644c601b953ba7715e093bfa10ca5ea97b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/198878
Run-TryBot: Ian Cottrell <52376736e5e84615ec49f9c1843b8acc178b1d8d@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools