Only report typed holes errors/warnings if no other errors remain

I often use typed holes while developing so I don't have to think about them while refactoring something. Unfortunately, `ghcide` (and most other tools) still flag the holes with warnings/errors unless you completely disable them. I think it would be great if you could (conditionally) make `ghcide` only report hole errors/warnings when all other issues have been fixed so they don't interrupt refactoring attempts with pointless noise.

(Actually, writing this I realise it might be even better to generalise this to entire sets of warnings that should only be reported when everything else is fixed, which could then include things like unused names/imports, but this might only be feasible after GHC finally gets structured error output...)