Simon Peyton Jones authored Mar 13, 2021 and Marge Bot committed Mar 31, 2021

This patch fixes a small but egregious bug, which allowed
a type signature like
    f :: forall a. blah
not to fail if (blah :: a).  Acutally this only showed
up as a ASSERT error (#19495).

The fix is very short, but took quite a bit of head scratching

Hence the long Note [Escaping kind in type signatures]

While I was in town, I also added a short-cut for the
common case of having no quantifiers to tcImplicitTKBndrsX.

Metric Decrease:
    T9198

Metric Increase:
    T9198