Fix incorrect memory layout on Rust >= 1.67.0

[pstuecker]

Since Rust 1.67.0, the Rust compiler groups fields in a struct if it improves alignment. See rust-lang/rust#102750 for details. Prior to that change, in some cases repr(Rust) and repr(C) structs had the same memory layout, which now differs, breaking C<=>Rust interfacing.

We've had a few instances in the code where we (implicitly) relied on the memory layout being equivalent to repr(C), which stopped some of the browser functions from working if compiled with a newer Rust version.

[github-actions]

License summary

❌ Not yet vetted dependencies:

Dependency	License	Status	Ticket
-/-/-/chromium/113.0.5672.93	unknown	restricted	none
-/-/chromiumembedded/cef/113.1.5	unknown	restricted	none

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Workflow run (with attached summary files):
https://github.com/eclipse-set/browser/actions/runs/6143753050