Rollup merge of #130496 - jder:issue-130400, r=compiler-errors

Fix circular fn_sig queries to correct number of args for methods

Fixes #130400. This was a [debug assert](https://github.com/rust-lang/rust/blob/28e8f01c2a2f33fb4214925a704e3223b372cad5/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs#L2557) added to some argument error reporting code in #129320 which verified that the number of params (from the HIR) matched the `matched_inputs` which ultimately come from ty::FnSig. In the reduced test case:

```
fn foo(&mut self) -> _ {
    foo()
}
```

There is a circular dependency computing the ty::FnSig -- when trying to compute it, we try to figure out the return value, which again depends on this ty::FnSig. In #105162, this was supported by short-circuiting the cycle by synthesizing a FnSig with error types for parameters. The [code in question](https://github.com/rust-lang/rust/pull/105162/files#diff-a65feec6bfffb19fbdc60a80becd1030c82a56c16b177182cd277478fdb04592R44) computes the number of parameters by taking the number of parameters from the hir::FnDecl and adding 1 if there is an implicit self parameter.

I might be missing a subtlety here, but AFAICT the adjustment for implicit self args is unnecessary and results in one too many args. For example, for this non-errorful code:

```
trait Foo {
    fn bar(&self) {}
}
```

The resulting hir::FnDecl and ty::FnSig both have the same number of inputs -- 1. So, this PR removes that adjustment and adds a test for the debug ICE.

r? `@compiler-errors`

0 files changed, 0 insertions, 0 deletions