Investigate whether it's beneficial to share P/Invokes with similar signatures

Example:

```cs
Messaging.void_objc_msgSend_IntPtr_nuint(base.Handle, Selector.GetHandle("setTitle:forState:"), intPtr, (nuint)(ulong)P_1);
```

`P_1` is a `[Native]` enum, which is an `n[u]int` so it can have a different size on 32/64 bits architectures.
An `IntPtr` can also do this job and since we're already using them in many places (handles) we have a better chance to share an existing signature for `objc_msg[Super]Send`
e.g. `void_objc_msgSend_IntPtr_IntPtr` already exists

Potential:

- smaller platform assembly (minor impact)
- smaller app bundles for large apps (minor impact)