'DynFlag'-free version of 'mkParserFlags'
Summary: This is a fixed version of the reverted d2fbc33c and 5aa29231.
Obtaining a DynFlags is difficult, making using the lexer/parser
for pure parsing/lexing unreasonably difficult, even with mkPStatePure.
This is despite the fact that we only really need
* language extension flags
* warning flags
* a handful of boolean options
The new mkParserFlags' function makes is easier to directly construct a
ParserFlags. Furthermore, since pExtsBitmap is just a footgun, I've gone
ahead and made ParserFlags an abstract type.
Also, we now export ExtBits and getBit instead of defining/exporting a
bunch of boilerplate functions that test for a particular 'ExtBits'.
In the process, I also
- cleaned up an unneeded special case for
ITstatic - made
UsePosPragsanother variant ofExtBits - made the logic in
reservedSymsFMmatch that ofreservedWordsFM
Test Plan: make test
Reviewers: bgamari, alanz, tdammers
Subscribers: sjakobi, tdammers, rwbarton, mpickering, carter
GHC Trac Issues: #11301
Differential Revision: https://phabricator.haskell.org/D5405