Refactor package flags into several distinct types.
Summary: Previously, all package flags (-package, -trust-package, -ignore-package) were bundled up into a single packageFlags field in DynFlags, under a single type. This commit separates them based on what they do. This is a nice improvement, because it means that Packages can then be refactored so that a number of functions are "tighter": - We know longer have to partition PackageFlags into the ignore flag and other flags; ignore flags are just put into their own field. - Trust flags modify the package database, but exposed flags do not (they modify the visibility map); now applyPackageFlag and applyTrustFlag have tighter signatures which reflect this. This patch was motivated by the need to have a separate visibility map for plugin packages, which will be in a companion patch. Signed-off-by: Edward Z. Yang <email@example.com> Test Plan: validate Reviewers: austin, bgamari, duncan Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1659