Let #[allow(unstable_name_collisions)] work for things other than function

[magurotuna]

Fixes #81522

In addition to the report in #81522, currently #[allow(unstable_name_collisions)] doesn't suppress the corresponding diagnostics even if this attribute is appended to an expression statement or a let statement. It seems like this is because the wrong HirId is passed to struct_span_lint_hir.
It's fixed in this PR, and a regression test for it is also added.

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[magurotuna]

Hmm, according to the CI, my fix doesn't work for macro invocations (so I made this PR drafted for now). But perhaps is it expected behavior? In fact, take the following as an example:

macro_rules! foo {
    ($i:ident) => {
        let $i = 42;
    };
}

fn main() {
    #[allow(unused_variables)]
    foo!(a);
}

#[allow(unused_variables)] in the above example doesn't suppress the lint diagnostic:

warning: unused variable: `a`
 --> src/main.rs:3:13
  |
3 |         let $i = 42;
  |             ^^ help: if this is intentional, prefix it with an underscore: `_a`
...
9 |     foo!(a);
  |     -------- in this macro invocation
  |
  = note: `#[warn(unused_variables)]` on by default
  = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

warning: 1 warning emitted

However, if the attribute is appended to main function like:

macro_rules! foo {
    ($i:ident) => {
        let $i = 42;
    };
}

#[allow(unused_variables)]
fn main() {
    foo!(a);
}

then it does suppress the lint!
So I'm wondering if I should take macro invocations into account in this PR or not... 😕

---

For now, I just deleted a test for macro invocation from issue-81522.rs. Please let me know if macro invocations should also be covered.

[matthewjasper]

Can this be self.scope_expr_id?

[magurotuna]

That's correct! Fixed it.

[matthewjasper]

@bors r+

[bors]

📌 Commit 06b3636 has been approved by matthewjasper

[bors]

⌛ Testing commit 06b3636 with merge 39eee17...