This will replace package_imports.
It has a BIGINT for the reference to unit_id, and switches to_path
from a string to a path id.
Change-Id: Ib2e50df2a7629fc202d993ae792890caee9c6d0e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/326130
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>