This change adds a Package interface to the source package, which allows
us to reduce the information cached per-package (we don't use any of the
unnecessary fields in a *go/packages.Package).
This change also adds an analysis cache for each package, which is used
to cache the results of analyses to avoid recomputation.
Change-Id: I56c6b5ed51126c27f46731c87ac4eeacc63cb81a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/165750
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
