Support template-haskell 2.17, plus unlifted fix.

[galenhuntington]

Most changes are to use the new Code newtype (https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3358).

Also, while I was in there I took the opportunity to fix #43.

Note that I had to use your explicit-specificity branch of th-abstraction to build, since it's a dependency. Bounds adjusted accordingly.

[RyanGlScott]

Thanks for the PR. Do note that I already have a quote branch in the works which aims to solve this same problem, but it performs some additional refactoring to minimize the amount of CPP that needs to be used.

[galenhuntington]

Ah, I didn't see that.

[galenhuntington]

From the looks of it, there's nothing new in this PR then, so I'll close.

[RyanGlScott]

Admittedly, branches aren't the most easily discoverable things. I've opened #45 with the current state of the quote branch to more widely advertise its existence. With luck, that branch should continue to work once GHC 9.0.1-alpha1 is released.