Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in rust-lang#79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: rust-lang#82679

Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in rust-lang#79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: rust-lang#82679

Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in rust-lang#79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: rust-lang#82679

Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in rust-lang#79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in rust-lang#79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: rust-lang#82679

Rollup of 10 pull requests

Successful merges:

 - rust-lang#82047 (bypass auto_da_alloc for metadata files)
 - rust-lang#82415 (expand: Refactor module loading)
 - rust-lang#82557 (Add natvis for Result, NonNull, CString, CStr, and Cow)
 - rust-lang#82613 (Remove Item::kind, use tagged enum. Rename variants to match)
 - rust-lang#82642 (Fix jemalloc usage on OSX)
 - rust-lang#82682 (Implement built-in attribute macro `#[cfg_eval]` + some refactoring)
 - rust-lang#82684 (Disable destination propagation on all mir-opt-levels)
 - rust-lang#82755 (Refactor confirm_builtin_call, remove partial if)
 - rust-lang#82857 (Edit ructc_ast_lowering docs)
 - rust-lang#82862 (Generalize Write impl for Vec<u8> to Vec<u8, A>)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup