Support `type()`'s functional syntax

[InSyncWithFoo]

(First raised on Discord.)

Currently ty doesn't understand type()'s functional syntax very well (playground):

# error: Object of type `type` is not assignable to `type[int]`
U32: type[int] = type('U32', (int,), {})

It understands type(...) returns a new type, but fails to take the bases into account.