gopls.mod files should take precedence over go.mod files when finding a
workspace root. To allow this, implement our own algorithm for expanding
the workspace, rather than using the go command.
For golang/go#41837
Change-Id: I943c08bdbdbdd164f108e44bae95d2c659a6e21e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/263897
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Trust: Robert Findley <rfindley@google.com>