Auto merge of #31461 - jseyfried:remove_import_resolutions, r=nrc

This PR adds to `NameBinding` so it can more fully represent bindings from imports as well from items, refactors away `Target`, generalizes `ImportResolution` to a simpler type `NameResolution`, and uses a single `NameResolution`-valued map in place the existing maps `children` and `import_resolutions` (of `NameBinding`s and `ImportResolution`s, respectively), simplifying duplicate checking and name resolution.

It also unifies the `resolve_name_in_module` in `lib.rs` with its namesake in `resolve_imports.rs`, clarifying and improving the core logic (fixes #31403 and fixes #31404) while maintaining clear future-comparability with shadowable globs (i.e., never reporting that a resolution is a `Success` or is `Failing` unless this would also be knowable with shadowable globs).

Since it fixes #31403, this is technically a [breaking-change], but it is exceedingly unlikely to cause breakage in practice. The following is an example of code that would break:
```rust
mod foo {
    pub mod bar {} // This defines bar in the type namespace
    pub use alpha::bar; // This defines bar in the value namespace

    // This should define baz in both namespaces, but it only defines baz in the type namespace.
    pub use self::bar as baz;
    pub fn baz() {} // This should collide with baz, but now it does not.
}

pub fn f() {}
mod alpha {
    pub use self::f as bar; // Changing this to `pub fn bar() {}` causes the collision right now.
    pub use super::*;
}
```

r? @nrc

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