Suggest using `as_mut()` and `as_ref()` instead of `(*ptr.as_ptr()).field` in unsafe Rust.

What it does

It suggests the developer to write cleaner code when using unsafe Rust. Rust has been critisized for (*ptr.as_ptr()).field syntax for accessing field in from a *mut T in unsafe Rust. Frankly, it looks horrible and many people are not aware the helper methods .as_mut() and .as_ref() on raw pointers.

Advantage

This will improve the developer experience when reading and writing unsafe rust code using raw pointers.

Drawbacks

Nothing that I can think of but I'd like to know if you find any!

Example

struct Node {
    elem: i32,
    next: Option<NonNull<Node>>
};

let node: NonNull<Node> = NonNull::new_unchecked(Node { elem: 10, next: None });

// Using longer syntax on right for demonstration
(*node.as_ptr()).elem = (*node.as_ptr()).elem * 2;

Could be written as:

// ...omitted

// notice `mut` here
let mut node = NonNull::new_unchecked(Node { elem: 10, next: None });

// Mutable and immutable access seperately
node.as_mut().elem = node.as_ref().elem * 2;

No implementation file or test is named; start by reading the examples in this issue and the 17-comment discussion to identify the intended lint scope and diagnostic behavior. Done means an agreed, tested Clippy lint for the unsafe raw-pointer field-access pattern and its suggested as_mut()/as_ref() form.