Update Cabal to HEAD, IPID renamed to Component ID.
This commit contains a Cabal submodule update which unifies installed package IDs and package keys under a single notion, a Component ID. We update GHC to keep follow this unification. However, this commit does NOT rename installed package ID to component ID and package key to unit ID; the plan is to do that in a companion commit. - Compiler info now has "Requires unified installed package IDs" - 'exposed' is now expected to contain unit keys, not IPIDs. - Shadowing is no more. We now just have a very simple strategy to deal with duplicate unit keys in combined package databases: if their ABIs are the same, use the latest one; otherwise error. Package databases maintain the invariant that there can only be one entry of a unit ID. Signed-off-by: Edward Z. Yang <email@example.com> Test Plan: validate Reviewers: simonpj, austin, bgamari, hvr, goldfire Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1184 GHC Trac Issues: #10714