This changes adds basic support for running `go mod tidy` as a code
action when a user opens a go.mod file. When we have a command
available like `go mod tidy -check`, we will be able to return edits as
part of the codeAction. For now, we execute the command directly.
This change also required a few modifications to our handling of file
kinds so that we could distinguish between a Go file and a go.mod file.
Change-Id: I343079b8886724b67f90a314e45639545a34f21e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/196322
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
