Update `hls-splice-plugin`

[fendor]

The splice plugin only compiles with GHC 9.6 and 9.8.

Let's update it to support at least GHC 9.14

[georgefst]

FWIW, I tried this a while back, and gave up due to lack of familiarity with the ghc-exactprint API, which has hopefully stabilised a bit by now: #4452