borrowck typeck children together with their root
This introduces new cycle errors, even with `feature(inline_const_pat)` removed, see the `non-structural-match-types-cycle-err.rs` test.
The new cycle error happens as the layout of `async`-blocks relies on their `optimized_mir`. As that now depends on `mir_borrowck` of its typeck parent, computing the layout of an `async`-block during MIR building, e.g. when evaluating a named `const` pattern. I think there's currently no way to have a named const pattern whose type references an async block while being allowed? cc `@oli-obk` `@RalfJung`
I cannot think of other cases where we currently rely on the MIR of a typeck children while borrowchecking their parent. The crater run came back without any breakage. My work here will prevent any future features which rely on this as we'll get locked into borrowchecking them together as I continue to work on https://github.com/rust-lang/types-team/issues/129, cc `@rust-lang/types.`
r? compiler-errors
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