Apply nothunks to ghcide and dependencies

[nothunks](http://hackage.haskell.org/package/nothunks) is a library to do runtime detection of unexpected thunks.
This is very relevant for us since we have suffered from space leaks in the past.

Thunks checking could be guarded by a flag. I expect that there will be plenty of thunks in ghcide, its dependencies and GHC itself. If we ever manage to eliminate all of them, we can enable the flag in the benchmark CI job and fail it when a new thunk is introduced.

Potential sources of thunks include:
- The values map
- The Shake state
- The diagnostics store
- The position mapping
- The Shake session queue