Investigate changing constructor of `BaseControl` to lessen restrictions on `threadBaseControlViaUnlift`

[KingoftheHomeless]

threadBaseControlViaUnlift requires that the relevant transformer is representational in the transformed monad,which is not satisfied by abstract monad transformers. A relevant use-case for removing this restriction is for haskeline's InputT, as shown in #14.

Two plausible approaches to solve this:

1. Make BaseControl MonadTransControl-based rather than MonadBaseControl-based
2. Inline the entire MonadBaseControl dictionary into BaseControl.

[KingoftheHomeless]

I forgot how the restrictions on coerce with abstract data types work -- abstract monad transformers are still considered representational if possible, unless the user explicitly type roles it as nominal.

This means this issue is far less important than I thought it was. Still desirable, but it no longer has a concrete use-case.