The partial snapshot/serializer/deserializer are renamed to context *,
while the partial snapshot cache is renamed to startup object cache in
line with the read-only object cache (as this better reflects where it
lives and what it does).

To avoid a gap in the file history due to renaming both the files and
identifiers simulataneously, this leaves all the partial-*.* files in
place. They will be renamed in a follow-up CL.

Bug: v8:10416
Change-Id: I5ef41cad751aaa24b35ee2b3c72bd0295832f2c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144115
Commit-Queue: Dan Elphick <delphick@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67306}