struct ClockTransformationLayoutCheck

The clock transformation for a mappable clock lives in a page which is shared

with (and read directly by) user mode: the VDSO reinterpret_casts the mapping

to a `fasttime::ClockTransformation

<Adapter

>`. See

//zircon/kernel/lib/userabi/vdso/zx_clock_read_mapped.cc,

//zircon/kernel/lib/userabi/vdso/zx_clock_get_details_mapped.cc, and

//src/starnix/kernel/vdso/vdso_calculate_utc.cc.

The only producer of that memory is the Rust `ClockTransformation` in

//zircon/kernel/object/clock_dispatcher.rs, which pins its own layout with a

matching set of assertions. The assertions below pin the C++ view of the

very same bytes, so that the two can never drift apart silently.