…iaskrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#134364 (Use E0665 for missing `#[default]` on enum and update doc)
 - rust-lang#134601 (Support pretty-printing `dyn*` trait objects)
 - rust-lang#134603 (Explain why a type is not eligible for `impl PointerLike`.)
 - rust-lang#134618 (coroutine_clone: add comments)
 - rust-lang#134630 (Use `&raw` for `ptr` primitive docs)
 - rust-lang#134637 (Flatten effects directory now that it doesn't really test anything specific)

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

Rollup merge of rust-lang#134364 - estebank:derive-docs, r=fmease

Use E0665 for missing `#[default]` on enum and update doc

The docs for E0665 when doing `#[derive(Default]` on an `enum` previously didn't mention `#[default]` at all, or made a distinction between unit variants, that can be annotated, and tuple or struct variants, which cannot.

E0665 was not being emitted, we now use it for the same error it belonged to before.

```
error[E0665]: `#[derive(Default)]` on enum with no `#[default]`
  --> $DIR/macros-nonfatal-errors.rs:42:10
   |
LL |   #[derive(Default)]
   |            ^^^^^^^
LL | / enum NoDeclaredDefault {
LL | |     Foo,
LL | |     Bar,
LL | | }
   | |_- this enum needs a unit variant marked with `#[default]`
   |
   = note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
help: make this unit variant default by placing `#[default]` on it
   |
LL |     #[default] Foo,
   |     ++++++++++
help: make this unit variant default by placing `#[default]` on it
   |
LL |     #[default] Bar,
   |     ++++++++++
```