Remove `QueryEngine` trait
This removes the `QueryEngine` trait and `Queries` from `rustc_query_impl` and replaced them with function pointers and fields in `QuerySystem`. As a side effect `OnDiskCache` is moved back into `rustc_middle` and the `OnDiskCache` trait is also removed.
This has a couple of benefits.
- `TyCtxt` is used in the query system instead of the removed `QueryCtxt` which is larger.
- Function pointers are more flexible to work with. A variant of https://github.com/rust-lang/rust/pull/107802 is included which avoids the double indirection. For https://github.com/rust-lang/rust/pull/108938 we can name entry point `__rust_end_short_backtrace` to avoid some overhead. For https://github.com/rust-lang/rust/pull/108062 it avoids the duplicate `QueryEngine` structs.
- `QueryContext` now implements `DepContext` which avoids many `dep_context()` calls in `rustc_query_system`.
- The `rustc_driver` size is reduced by 0.33%, hopefully that means some bootstrap improvements.
- This avoids the unsafe code around the `QueryEngine` trait.
r? `@cjgillot`
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