Use a bit queue to implement `alterF` for `Data.Map`. This is fairly
competitive with the simple implementation in `Control.Lens.At`
even with `Int` keys. For keys that are more expensive to compare,
it should be substantially better. In case of extremely large maps
that would overflow the bit queue, this falls back to a slower,
Yoneda-based, implementation. This code is disabled when the word
size is at least 61, as maps with nearly a quadrillion entries seem
somewhat unlikely.

Add rules to specialize to `Const` and `Identity` functors.

Add QuickCheck properties to supplement the unit tests, including
ones that should trigger the rewrite rules and ones that should not.

Remove some more pre-7.0 junk.