Add an autocompletion implementation to the LSP. Also, add a function
that type-checks a package at a certain position, returning an *ast.File
and token.Pos for querying completion.
Change-Id: I288d4e6ed168e6014e79a4436f31f5b4a99b7139
Reviewed-on: https://go-review.googlesource.com/c/147657
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
