A same-shape requirement 'length(T...) == length(U...)' becomes a rewrite
rule 'T.[shape] => U.[shape]'. Reduced shape rules will drop the [shape]
term from each side of the rule, and create a same-shape requirement
between the two type parameter packs.
The Requirement Machine operates on canonical types internally and erases
sugared types appearing in generic requirements as a result.
For trivial cases like Array<T> vs [T], we can use the existing
TypeBase::reconstituteSugar() utility to produce a more aesthetically-pleasing
generic signature.
The final step in minimization is building Requirements and
ProtocolTypeAliases from the minimal Rules in the RewriteSystem.
Move this to a new file and refactor it a bit to handle
Requirements and ProtocolTypeAliases more consistently.
