Auto merge of #136776 - BoxyUwU:forbid_object_lifetime_casts, r=lcnr

Forbid freely casting lifetime bounds of dyn-types

Fixes rust-lang/rust#136702

Reference PR:

- rust-lang/reference#1951

Background reading about VTable calls/dyn compatibility: https://hackmd.io/zUp-sgZ0RFuFgsNfD4JqYw

This PR causes us to start enforcing that lifetimes of dyn types are constrained through pointer casts. Currently on stable casting `*mut dyn Trait + 'a` to `*mut dyn Trait + 'b` passes with no requirements on `'a` or `'b`. Under this PR we now require `'a` to outlive `'b`.

Even though the pointee of `*mut` pointers is considered to be invariant, we still use subtyping rather than equality. This mirrors how we support coercing `&mut dyn Trait + 'a` to `&mut dyn Trait + 'b` while requiring only `'a: 'b`. I believe this coercion is sound as there is no way for safe code to `mem::swap` two `dyn Trait`'s, and the same is definitely true of raw pointers.

See the changes to this test: https://github.com/rust-lang/rust/pull/136776/files#diff-5523f20a800287a89c9f3e92646c887f3f7599be006b29dd9315f734a2137764

We also do not enforce any constraints on the lifetime of the dyn types if there are multiple pointer indirections. For example `*mut *mut dyn Trait + 'a` is allowed to be casted to `*mut *mut dyn Trait + 'b` with no requirements on `'a` or 'b`. This case is just a normal thin pointer cast where we do not care about the pointee type as there is no VTable in play.

Test: https://github.com/rust-lang/rust/pull/136776/files#diff-3b6c8da342bb6530524158d686455a545bb8fd6f59cf5ff50d1d991ce74c9649

Finally, this is about *any* cast where the pointee is *unsized* with dyn-type metadata, not just *literally* the pointee type being a dyn-type. E.g. casting `*mut Wrapper<dyn Trait + 'a>` to `*mut Wrapper<dyn Trait + 'b>` requires `'a: 'b` under this PR.

Test: https://github.com/rust-lang/rust/pull/136776/files#diff-ca0c44df62ae1ad1be70f892f01a59714336c7baf78602a5887ac1cf81145c96

### Breakage

This is a breaking change.
Crater Report Comment: rust-lang/rust#136776 (comment)
Generated Report: https://crater-reports.s3.amazonaws.com/pr-136776-2/index.html

The majority of the breakage is caused by the `metrics` crate with 142 of the regressions, and the `may` crate with 14 of the regressions. The `metrics` crate has been fixed and has backported the fix to previous versions of the crate that were also affected. The`may` crate has also been fixed.

PRs against affected crates have been opened and can be seen here:
- belalang-project/belalang#6
- tyilo/multi-vec#1
- luksan/lox#1
- pfzetto/bring-your-own-memory-demo#1
- vitorhnn/bfr#1
- gipsyh/PPSMC#1
- orengine/orengine#33
- maroider/async_scoped_task#1
- WorldSEnder/scoped_worker_thread#1
- Wind-Corporation/trapiron#5
- Thombrom/snek#1
- Xudong-Huang/may#113
- metrics-rs/metrics#564
- DouglasDwyer/micropool#1
- Magicolo/phylactery#8
- HellButcher/pulz#29
- UxuginPython/rrtk#1
- wvwwvwwv/scalable-delayed-dealloc#4
- ultimaweapon/tsuki#32

There were six regressions I've not filed PRs against:
- https://github.com/weiznich/diesel_benches depends on a ~6year old version of diesel (where the regression is)
- https://crates.io/crates/cogo/0.1.36 is an old version of cogo, since that release cogo has already been updated to not depend on pattern this PR breaks
- https://github.com/cruise-automation/webviz-rust-framework is an archived read only repo so 🤷‍♀️
- makepad_render, doesn't seem to have source available and is 6 years old 🤷‍♀️
- outsource-heap - not on github
- zaplib - I couldn't get it to compile locally as it failed to compile a dependency

r? `@ghost`

Author: bors