Embed CoreToLogic.lg into liquidhaskell-boot

[facundominguez]

Currently, the LiquidHaskell plugin searches for CoreToLogic.lg in the installation of the liquidhaskell package. This makes a bit more fiddly to handle tests that run without installing LiquidHaskell because then we need to set here and there an environment variable liquidhaskell_boot_datadir to point at the file at runtime.

Unless someone has a use case for modifying CoreToLogic.lg after liquidhaskell is built, I would like to have it embedded in the source code instead, perhaps via Template Haskell or quasi quotations.