Allow bracketed expressions in ZenType declarations.

[eutro]

This can reduce ambiguity and possibly allow for function arrays, or associatives with function values, if ZenTypeFunctionCallable#toJavaClass ever gets implemented.

[eutro]

Without the parentheses, stringifying (function()int)[] would become function()int[], though, which is not the same.

Brackets are a common thing to group expressions, so I don't think people will be too confused, though I'll admit it might look ugly.

[eutro]

It might make sense to have ZenTypeFunction stringify including the parentheses instead, since it's the only type where it makes a difference.