Uplift clippy::invalid_utf8_in_unchecked lint

[Urgau]

This PR aims at uplifting the clippy::invalid_utf8_in_unchecked lint into two lints.

invalid_from_utf8_unchecked

(deny-by-default)

The invalid_from_utf8_unchecked lint checks for calls to std::str::from_utf8_unchecked and std::str::from_utf8_unchecked_mut with an invalid UTF-8 literal.

Example

unsafe {
    std::str::from_utf8_unchecked(b"cl\x82ippy");
}

Explanation

Creating such a str would result in undefined behavior as per documentation for std::str::from_utf8_unchecked and std::str::from_utf8_unchecked_mut.

invalid_from_utf8

(warn-by-default)

The invalid_from_utf8 lint checks for calls to std::str::from_utf8 and std::str::from_utf8_mut with an invalid UTF-8 literal.

Example

std::str::from_utf8(b"ru\x82st");

Explanation

Trying to create such a str would always return an error as per documentation for std::str::from_utf8 and std::str::from_utf8_mut.

---

Mostly followed the instructions for uplifting a clippy lint described here: #99696 (review)

@rustbot label: +I-lang-nominated
r? compiler

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For Clippy:

changelog: Moves: Uplifted clippy::invalid_utf8_in_unchecked into rustc