[roll] Roll fuchsia [zircon] Add zx_sampler_* syscalls

Adds a group of @next only syscall to mark a thread to have its stack
periodically sampled and written to a buffer.

The general flow looks like:
- Use zx_sampler_create to set up a session and get buffers that will be
  written to
- Call zx_sampler_attach on each relevant thread to enable sampling
- Take some samples
- Call zx_sampler_stop to disable sampling
- Map the assigned buffers and read out the written data

Calling zx_sampler_attach  marks a thread to be sampled
periodically as described in a passed in config. This comes with some
complications since sampling the thread requires reading user memory
which isn't always safe to do from a timer context.

Rather than immediately attempting to read the thread's user stack, we
set a new thread signal `THREAD_SIGNAL_SAMPLE_STACK`. This indicates to
the thread that the next time it's in a safe spot to do so, it should
walk its stack and write it out to the buffer assigned to its core.

Original-Bug: b/301632554
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/933215
Original-Revision: 0c017e8360a82d135d45c17decdbe8851d2ce0c2
GitOrigin-RevId: 34f5be5734aa9200da85bb208a91ba340b342d4e
Change-Id: I5074799ba84f4c432eea1540585d881d38945c09