Rollup merge of #93038 - GuillaumeGomez:block-doc-comments, r=notriddle

Rollup merge of #93038 - GuillaumeGomez:block-doc-comments, r=notriddle

Fix star handling in block doc comments

Fixes #92872.

Some extra explanation about this PR and why https://github.com/rust-lang/rust/pull/92357 created this regression: when we merge doc comment kinds for example in:

```rust
/// he
/**
* hello
*/
#[doc = "boom"]
```

We don't want to remove the empty lines between them. However, to correctly compute the "horizontal trim", we still need it, so instead, I put back a part of the "vertical trim" directly in the "horizontal trim" computation so it doesn't impact the output buffer but allows us to correctly handle the stars.

r? `@camelid`