Change regex-posix -> regex-tdfa

[phadej]

regex-posix is just broken (on Windows), that's what I heard from @RyanGlScott

[RyanGlScott]

Don't just take it from me! The Cabal developers have also struggled with regex-posix, and this Cabal issue is where I first heard it from.

Another benefit of using regex-tdfa is that it's more GHCJS-compatible due to its lack of C dependencies. Of course, that's just a perk—not working correctly at all on Windows is arguably a more serious issue.

[hvr]

I briefly discussed this with Ryan; since regex-tdfa has issues of its own so that it doesn't qualify as a strictly better replacement for regex-posix, and I've coincidentally started the take-over process for the regex-posix package motivated by this and other packages I maintain (without being aware of this ticket), the plan is to fix the issues with regex-posix which occur on C-FFI capable platforms (and where regex-posix has clear benefits), as well as providing the ability to switch to regex-tdfa in test-framework for targets where regex-tdfa is a necessary evil; this plan should allow us to combine best-of-both-worlds approach, while addressing the concerns stated.