Add support for reborrowing pinned method receivers
This builds on #130526 to add pinned reborrowing for method receivers. This enables the folllowing examples to work:
```rust
#![feature(pin_ergonomics)]
#![allow(incomplete_features)]
use std::pin::Pin;
pub struct Foo;
impl Foo {
fn foo(self: Pin<&mut Self>) {
}
fn baz(self: Pin<&Self>) {
}
}
pub fn bar(x: Pin<&mut Foo>) {
x.foo();
x.foo();
x.baz(); // Pin<&mut Foo> is downgraded to Pin<&Foo>
}
pub fn baaz(x: Pin<&Foo>) {
x.baz();
x.baz();
}
```
This PR includes the original one, which is currently in the commit queue, but the only code changes are in the latest commit (d3c53aaa5c6fcb1018c58d229bc5d92202fa6880).
#130494
r? `@compiler-errors`
68de7d11a9