This change moves gopls from type-checking packages using the
go/packages API to type-checking from source. This is the first step in
adding caching to gopls.
Change-Id: I2a7dcfd8c9c0bfc6c35c86eadcdc6f9ce53d9be7
Reviewed-on: https://go-review.googlesource.com/c/161497
Reviewed-by: Ian Cottrell <iancottrell@google.com>