This change moves the facts package so that it can be reused by gopls.
It remains a tools-internal API.
A forthcoming reimplementation of gopls's analysis driver will
make use of the new packages and the features mentioned below.
Also:
- change parameter of read() callback from 'path string' to *Package.
- use NewDecoder().Decode() to amortize import-map computation across calls.
Change-Id: Id10cd02c0c241353524d568d5299d81457f571f8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/444796
Reviewed-by: Tim King <taking@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>
d6511e5e9f