This pulls both classes into a dedicated file. InstructionStream may
be removed in a follow-up.

Tbr: mlippautz@chromium.org
Bug: v8:6666
Change-Id: Ibd374eba25cebf7495390ec13f6b4aeac5e1dc01
Reviewed-on: https://chromium-review.googlesource.com/c/1337738Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57562}