Make PlaceholderReplacer shallow_resolver and recur when infer vars
This makes resolve type and const infer vars resolve.
Given:
```rust
#![feature(inherent_associated_types)]
#![allow(incomplete_features)]
struct Foo<T>(T);
impl<'a> Foo<fn(&'a ())> {
type Assoc = &'a ();
}
fn bar(_: for<'a> fn(Foo<fn(Foo<fn(&'static ())>::Assoc)>::Assoc)) {}
fn main() {}
```
We should normalize `for<'a> fn(Foo<fn(Foo<fn(&'static ())>::Assoc)>::Assoc)` to `for<'0> fn(&'1 ())` with `'1 == '0` and `'0 == 'static` constraints. We have to resolve `'1` to `'static` in the infcx associated to `PlaceholderReplacer`.
This is part of https://github.com/rust-lang/rust/pull/118118 but unrelated to that PR.
r? `@compiler-errors` `@lcnr`
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