Auto merge of rust-lang#120019 - lcnr:fn-wf, r=BoxyUwU

fix fn/const items implied bounds and wf check (rebase)

A rebase of rust-lang#104098, see that PR for discussion. This is pretty much entirely the work of `@aliemjay.` I received his permission for this rebase.

---

These are two distinct changes (edit: actually three, see below):
1. Wf-check all fn item args. This is a soundness fix.
Fixes rust-lang#104005

2. Use implied bounds from impl header in borrowck of associated functions/consts. This strictly accepts more code and helps to mitigate the impact of other breaking changes.
Fixes rust-lang#98852
Fixes rust-lang#102611

The first is a breaking change and will likely have a big impact without the the second one. See the first commit for how it breaks libstd.

Landing the second one without the first will allow more incorrect code to pass. For example an exploit of rust-lang#104005 would be as simple as:
```rust
use core::fmt::Display;

trait ExtendLt<Witness> {
    fn extend(self) -> Box<dyn Display>;
}

impl<T: Display> ExtendLt<&'static T> for T {
    fn extend(self) -> Box<dyn Display> {
        Box::new(self)
    }
}

fn main() {
    let val = (&String::new()).extend();
    println!("{val}");
}
```

The third change is to to check WF of user type annotations before normalizing them (fixes rust-lang#104764, fixes rust-lang#104763). It is mutually dependent on the second change above: an attempt to land it separately in rust-lang#104746 caused several crater regressions that can all be mitigated by using the implied from the impl header. It is also necessary for the soundness of associated consts that use the implied bounds of impl header. See rust-lang#104763 and how the third commit fixes the soundness issue in `tests/ui/wf/wf-associated-const.rs` that was introduces by the previous commit.

r? types

Author: bors