Auto merge of #58305 - scalexm:chalk-continued, r=nikomatsakis

(WIP) Small fixes in chalkification

Small fixes around region constraints and builtin impls. There are still some type inference errors, for example the following code errors out:
```rust
fn main() {
    let mut x: Vec<i32> = Vec::new();
    //                    ^^^^^^^^ cannot infer type for `std::vec::Vec<_>`
}
```
but explicitly specifying `Vec::<i32>::new` works.

With these few fixes, the following code now passes type-checking:
```rust
fn main() {
    let mut x: Vec<i32> = Vec::<i32>::new();
    x.push(5);
    println!("{:?}", x);
}
```

I also fixed the implied bounds bug as discussed on Zulip and in https://github.com/rust-lang-nursery/chalk/pull/206

cc @tmandry
r? @nikomatsakis

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