`offset_of!` ecosystem testing

[est31]

I'm filing this issue to get some testing of the offset_of macro, whose implementation has recently been merged in #106934 .

There is already widespread use of the offset_of macro in the ecosystem through an implementation supporting stable via the memoffset crate, whose version 0.9.0 supports the unstable_offset_of feature due to Gilnaa/memoffset#72. So for a lot of the users, testing out is as simple as updating memoffset and running the tests with the unstable_offset_of feature enabled. Thankfully, for testing one doesn't have to add that feature to Cargo.toml, creating a requirement on nightly, one can just add --features memoffset/unstable_offset_of and it will work.

The biggest reverse dependencies of memoffset are:

• crossbeam-epoch: PR
• nix: PR
• rustix: PR
• pyo3: PR comment
• wayland-sys: PR
• wasmtime-runtime: PR comment
• wasmer-types/wasmer-vm
• field-offset: PR comment
• rowan: PR
• glium: PR comment
• intrusive-collections: PR
• imgui: PR
• egui-glow: PR
• virtio-queue: comment
• arcstr: PR
• ggez

It would be good to go through this list, and:

1. update the memoffset crate to 0.9.0, ideally filing a PR (but not enabling unstable_offset_of in Cargo.toml unless the project already requires nightly!)
2. run cargo +nightly test --features memoffset/unstable_offset_of or cargo +nightly run --features memoffset/unstable_offset_of etc, trying out the feature and seeing if something is broken, ideally also the --all parameter if it's a workspace
3. tell here about the experience

In addition of that, it is useful to get feedback from any project that uses the memoffset crate indirectly as a transitive dependency. For that, one also has to wait for the upgrade to 0.9.0 to go through the dependency chain and then one can add a direct (unused) dependency on memoffset to enable the feature, and test it out.

For example, field-offset has a large number of reverse dependencies that one could go through also. I have made a PR for rustc in #112298.

cc #106655 tracking issue

[est31]

@rustbot label F-offset_of

[est31]

@rustbot label E-help-wanted