[roll] Roll fuchsia [starnix] Extend extended_pstate syscall test.

This change extends the `extended_pstate_test` suite to cover all
of the vector and other extended registers that might be perturbed
by Starnix's code after a restricted exit. Before this change, only
caller-saved registers were tested which meant that we did not have
a mechanism to detect cases where a page fault clobbered a callee-
saved register.

Specifically:
* `RegistersValue` becomes architecture-specific and large enough to
  hold the full register set for `x86_64` (16 XMM), `arm` (32 D),
  `aarch64` (32 Q), and `riscv64` (32 F + 32 V).
* Updated `SetTestRegisters`, `GetTestRegisters`, and
  `GetTestRegistersFromUcontext` to perform bulk loads/stores of the
  full register files.
* Updated `extended_pstate_initial_state_child.cc` to initialize and
  verify the entire register file to ensure registers are zeroed upon
  process initialization.
* Updated test cases to assert on the expanded register set.

The tests are currently failing on arm64/arm32, a follow-up change will
address the underlying bug here.

Original-Bug: 491848090
Multiply: extended_pstate
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1554703
Original-Revision: 543493de25af655caa6b6f9a71f7de9f239a43e0
GitOrigin-RevId: 253c20fdf14a0eb046392028c8be6aac2c6f3295
Change-Id: Ic25e884fd35c2402ff1b8e6c6171e203f8b6e3ce