Rollup merge of #78626 - fusion-engineering-forks:deprecated-trait-impl, r=estebank

Improve errors about #[deprecated] attribute

This change:

1. Turns `#[deprecated]` on a trait impl block into an error, which fixes #78625;
2. Changes these and other errors about `#[deprecated]` to use the span of the attribute instead of the item; and
3. Turns this error into a lint, to make sure it can be capped with `--cap-lints` and doesn't break any existing dependencies.

Can be reviewed per commit.

---
Example:
```rust
struct X;

#[deprecated = "a"]
impl Default for X {
    #[deprecated = "b"]
    fn default() -> Self {
        X
    }
}
```

Before:
```
error: This deprecation annotation is useless
 --> src/main.rs:6:5
  |
6 | /     fn default() -> Self {
7 | |         X
8 | |     }
  | |_____^
```

After:
```
error: this `#[deprecated]' annotation has no effect
 --> src/main.rs:3:1
  |
3 | #[deprecated = "a"]
  | ^^^^^^^^^^^^^^^^^^^ help: try removing the deprecation attribute
  |
  = note: `#[deny(useless_deprecated)]` on by default

error: this `#[deprecated]' annotation has no effect
 --> src/main.rs:5:5
  |
5 |     #[deprecated = "b"]
  |     ^^^^^^^^^^^^^^^^^^^ help: try removing the deprecation attribute
```

compiler/rustc_expand/src/base.rs

@@ -793,7 +793,7 @@ impl SyntaxExtension {
             allow_internal_unsafe: sess.contains_name(attrs, sym::allow_internal_unsafe),
             local_inner_macros,
             stability,
-            deprecation: attr::find_deprecation(&sess, attrs, span),
+            deprecation: attr::find_deprecation(&sess, attrs).map(|(d, _)| d),
             helper_attrs,
             edition,
             is_builtin,