Fix name resolution in lexical scopes
Currently, `resolve_item_in_lexical_scope` does not check the "ribs" (type parameters and local variables). This can allow items that should be shadowed by type parameters to be named.
For example,
```rust
struct T { i: i32 }
fn f<T>() {
let t = T { i: 0 }; // This use of `T` resolves to the struct, not the type parameter
}
mod Foo {
pub fn f() {}
}
fn g<Foo>() {
Foo::f(); // This use of `Foo` resolves to the module, not the type parameter
}
```
This PR changes `resolve_item_in_lexical_scope` so that it fails when the item is shadowed by a rib (fixes#32120).
This is a [breaking-change], but it looks unlikely to cause breakage in practice.
r? @nikomatsakis
06074ac004