Allow moving out of `&'static mut T`

Hello, it is perfectly sound to move out of &'static mut T and have that reference consumed, as no safe code can access T under the reference after that point.

struct NotDefaultNotCopy([u8; 20]);

fn main() {
    let foo: &'static mut NotDefaultNotCopy = Box::leak(Box::new(NotDefaultNotCopy([0; 20])));
    let foo_taken = *foo;

    println!("{:?}", foo_taken.0);
}

For example, miri is happy with that code if take in unsafely written (but detects leak) playground

Here is code with more unsafe but with no miri leak warnings: playground

The issue provides Rust reproductions and Rust Playground links demonstrating the proposed move from &'static mut T. Start by investigating the compiler's handling of moves out of mutable references and determine what focused compiler tests are needed; done means the demonstrated non-Copy move is accepted with sound behavior.