Add Shrinker to QuickChick for Terms and FTypes about cofq

[Chobbes]

Some shrinkers have been added. There's one that does not preserve the types of terms, and one that does.

The one that preserves types just does beta reduction (and makes sure the resulting term is smaller, which might actually make it not trigger very often).

Shrinkers could still be improved, and probably should be because the counterexamples we're getting are ridiculous:

(λ <Int>-><Int->Int, forall Int, <Int->Int>, <Int->Int, <>, <Int>, <Int, Int, Int>>> <Int>. (λ Int-><Int->Int, forall Int, <Int->Int>, <Int->Int, <>, <Int>, <Int, Int, Int>>> Int. if0 v1 then <λ Int->Int Int. v3, Λ. 2, <λ Int->Int Int. v1>, <λ Int->Int Int. v3, v3, <v1>, v3>> else (λ <Int->Int, forall Int, <Int->Int>, <Int->Int, <>, <Int>, <Int, Int, Int>>>-><Int->Int, forall Int, <Int->Int>, <Int->Int, <>, <Int>, <Int, Int, Int>>> <Int->Int, forall Int, <Int->Int>, <Int->Int, <>, <Int>, <Int, Int, Int>>>. <λ Int->Int Int. v1, Λ. -1, <λ Int->Int Int. 4>, <λ Int->Int Int. v5, v1, v5, v5>>) v0 (v1 - 1)) 3) if0 -1 then <4> else <2>