Filter orphan rules based on imports, fixes #10294 and #10420.
Summary: If we have an orphan rule in our database, don't apply it unless the defining module is transitively imported by the module we are processing. We do this by defining a new RuleEnv data type which includes both the RuleBase as well as the set of visible orphan modules, and threading this through the relevant environments (CoreReader, RuleCheckEnv and ScEnv). This is analogous to the instances fix we applied in #2182 4c834fdd , but done for RULES. An important knock-on effect is that we can remove some buggy code in LoadInterface which tried to avoid loading interfaces that were loaded by plugins (which sometimes caused instances and rules to NEVER become visible). One note about tests: I renamed the old plugins07 test to T10420 and replaced plugins07 with a test to ensure that a plugin import did not cause new rules to be loaded in. Signed-off-by: Edward Z. Yang <email@example.com> Test Plan: validate Reviewers: simonpj, austin, goldfire Subscribers: bgamari, thomie Differential Revision: https://phabricator.haskell.org/D950 GHC Trac Issues: #10420