Rollup merge of rust-lang#42052 - kennytm:fix-42007-ice-on-decode-lint-id, r=nikomatsakis

Refactor: Move the mutable parts out of LintStore. Fix rust-lang#42007.

* rust-lang#42007 happens because the `Session` `LintStore` is emptied when linting.
* The `Session` `LintStore` is emptied because the checker (`Early`/`LateContext`) wants ownership.
* The checker wants ownership because it wants to mutate the pass objects and lint levels.

The ownership of the whole store is not essential, only the lint levels and pass objects need to be owned. Therefore, these parts are extracted out of the `LintStore` into a separate structure `LintSession`. The "check crates" methods can operate on `&mut LintSession` instead of `&mut LintStore`.

This is a minor *breaking change* for lint writers since the `LintContext` trait is changed: the `mut_lints` and `level_stack` methods are removed. But no one outside of `librustc/lint/context.rs` is using these functions, so it should be safe.

Author: Mark-Simulacrum