Auto merge of #46664 - mikeyhew:raw_pointer_self, r=arielb1

arbitrary_self_types: add support for raw pointer `self` types

This adds support for raw pointer `self` types, under the `arbitrary_self_types` feature flag. Types like `self: *const Self`, `self: *const Rc<Self>`, `self: Rc<*const Self` are all supported. Object safety checks are updated to allow`self: *const Self` and `self: *mut Self`.

This PR does not add support for `*const self` and `*mut self` syntax. That can be added in a later PR once this code is reviewed and merged.

#44874

r? @arielb1