This moves the platform-specific WriteByteChunk (& friends) into
platform-specific embedded file writers.

Bug: v8:9103
Change-Id: I0113c90dbf661a39dabe62b420cf6a160ee1be1d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1631412
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61852}