Draft: Add -fcompact-holes
Summary: This adds a -fcompact-holes flag that prints typed hole error messages in a more compact format.
Also adds a user guide entry for the flag and test cases.
Reviewers: bgamari, RyanGlScott, tdammers
Subscribers: tdammers, rwbarton, carter
Differential Revision: https://phabricator.haskell.org/D5352