Remove the return_address intrinsic.

This intrinsic to get the return pointer was introduced in #16248 / #16081 by @pcwalton for Servo.
However, as explained in #34227, it's impossible to ensure it's used correctly, and it broke with `-Zorbit`.

Servo's usage is being replaced in servo/servo#11872, and I expect nobody else to have abused it.
But I've also started a crater run, just in case this is a `[breaking-change]` for anyone else.

internal: Add proc-macro-test crate back to the main workspace

Should fix rust-lang/rust-analyzer#16194

…ializers (rust-lang#16248)

When the initializer is a function call or suffixed literal (e.g.,
`size_of::<T>()` or `10u8`), suggest casting the initializer too, since
changing only the type annotation would fail to compile. Fixes
rust-lang/rust-clippy#16240

```
changelog: [`needless_type_cast`]: Fix suggesting invalid code for non-literal initializers
```