This allows us to write the lsp verbs in terms of a stable underlying source
management layer.
This should make it easier to refactor the underlying layer to add more powerful
caching and incremental modes as we go.
Change-Id: Iab97b061d80394a6fa6748a93a4c68f2deb46129
Reviewed-on: https://go-review.googlesource.com/c/147201
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
