This adds one more test that should track improvements to generator
layout, like #62958 and #62575.
In particular, this test highlights suboptimal layout, as the storage
for the argument future is not being reused across its usage as `upvar`,
`local` and `awaitee` (being polled to completion).
Especially when trying to diagnose runaway future sizes, it might be
more intuitive to sort the variants according to the control flow
(aka their yield points) rather than the size of the variants.
