Replace the ghc-lib flag with a subcomponent

[pepeiborra]

Addresses #1376 by creating a subcomponent hlint:ghclib that replaces the ghc-lib flag. This enables other packages upstream to declaratively select which "version" of hlint they need, e.g. HLS: pepeiborra/ide@637aa0b

A priori, there is no downside to introducing the ghclib component:

1. Building the hlint binary doesn't pull the ghclib component
2. No additional Hackage upload required

But there might be some hidden costs. Most tooling struggles with Cabal subcomponents. I don't know if stack can handle them, for instance.

[shayne-fletcher]

@pepeiborra #1410 has been accepted that flips the ghc-lib flag default to True. given past discussions i think then we might choose to abandon this PR now and close it out?