Fix BinOp `ty()` assertion and `fn_sig()` for closures
`BinOp::ty()` was asserting that the argument types were primitives. However, the primitive check doesn't include pointers, which can be used in a `BinaryOperation`. Thus extend the arguments to include them.
Since I had to add methods to check for pointers in TyKind, I just went ahead and added a bunch more utility checks that can be handy for our users and fixed the `fn_sig()` method to also include closures.
`@compiler-errors` just wanted to confirm that today no `BinaryOperation` accept SIMD types. Is that correct?
r? `@compiler-errors`
d67e80f12d