This CL fixes redesigns the current API, which does not correctly
manage lifetimes of the shared object conveyors.

See design doc at
https://docs.google.com/document/d/1TV6agY9dafVJFvdPrUAGbEvos8wL2WDnsmf84n3OJVU/edit?usp=sharing

This CL also removes the incorrect behavior of serializing all shared
strings by sharing instead of copying. Shared strings may be sent to
another process, which should still work.

Bug: v8:12547
Change-Id: I7413abd2d871fd3d52c9b433445cfa1d03e4a732
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3868713
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83044}