Rollup merge of rust-lang#144059 - LorrensP-2158466:remove-crate-loader, r=petrochenkov

Refactor `CrateLoader` into the `CStore`

Removes the `CrateLoader` and moves the code to `CStore`. Now, if you want to use the `CrateLoader`, you can just use `CStore`.

Should we rename `creader.rs` to `cstore.rs`?

r? ``@petrochenkov``

Author: matthiaskrgr