These tend to have special handling in a bunch of places anyway, so the variant helps remember that.  And I think it's easier to grok than non-Scalar Aggregates sometimes being `Immediates` (like I got wrong and caused 109992).  As a minor bonus, it means we don't need to generate poison LLVM values for them to pass around in `OperandValue::Immediate`s.

fix comment on Allocator trait

fixes rust-lang#107040

…ompiler-errors

Add a distinct `OperandValue::ZeroSized` variant for ZSTs

These tend to have special handling in a bunch of places anyway, so the variant helps remember that.  And I think it's easier to grok than `Aggregate`s sometimes being `Immediates` (after all, I previously got that wrong and caused rust-lang#109992).  As a minor bonus, it means we don't need to generate poison LLVM values for ZSTs to pass around in `OperandValue::Immediate`s.

Inspired by rust-lang#110021 (comment), so
r? ``@compiler-errors``

…cked, r=WaffleLapkin

Uplift `clippy::invalid_utf8_in_unchecked` lint

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

```rust
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

```rust
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: rust-lang#99696 (review)

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

-----

For Clippy:

changelog: Moves: Uplifted `clippy::invalid_utf8_in_unchecked` into rustc

…alfJung

Print a backtrace in const eval if interrupted

Demo:
```rust
#![feature(const_eval_limit)]
#![const_eval_limit = "0"]

const OW: u64 = {
    let mut res: u64 = 0;
    let mut i = 0;
    while i < u64::MAX {
        res = res.wrapping_add(i);
        i += 1;
    }
    res
};

fn main() {
    println!("{}", OW);
}
```
```
╭ ➜ ben@archlinux:~/rust
╰ ➤ rustc +stage1 spin.rs
^Cerror[E0080]: evaluation of constant value failed
 --> spin.rs:8:33
  |
8 |         res = res.wrapping_add(i);
  |                                 ^ Compilation was interrupted

note: erroneous constant used
  --> spin.rs:15:20
   |
15 |     println!("{}", OW);
   |                    ^^

note: erroneous constant used
  --> spin.rs:15:20
   |
15 |     println!("{}", OW);
   |                    ^^
   |
   = note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.
```

…lor-9, r=notriddle

Migrate GUI colors test to original CSS color format

Follow-up of rust-lang#111459.

The `browser-ui-test` update is a fix when converting the alpha value to hex format. More information [here](GuillaumeGomez/browser-UI-test#511).

r? ``@notriddle``