Tidy: Expose unfoldings if they take dictionary arguments by default.

Add the flag `-fexpose-overloaded-unfoldings` to be able to control this
behaviour with is on by default with `-O`.

For ghc's boot libraries file size grew by less than 1%.

-------------------------
Metric Decrease:
    MultiLayerModulesTH_OneShot
Metric Increase:
    T12425
    T13386
    hard_hole_fits
-------------------------