internal/lsp: correctly apply file edits for edit go directive
internal/lsp: correctly apply file edits for edit go directive

Fixes a bug where the go mod edit -go=version file edits
are never actually applied.

Change-Id: Id055b0fad3399a00e1245556eb39073f15be09d9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/389216
Trust: Suzy Mueller <a1fd7fee333bfb1457f0c89ab258f70a76be3c5d@golang.org>
Run-TryBot: Suzy Mueller <a1fd7fee333bfb1457f0c89ab258f70a76be3c5d@golang.org>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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