Use the `fuchsia_component` and `fuchsia_package` GN templates from the
Fuchsia SDK to package the `v8_unittests` test for Fuchsia. Give the
`v8_unittests` their own dedicated `.cmx` file, instead of depending on
`v8.cmx`.

Bug: chromium:1256503
Change-Id: I22788359bed18eb643e288ee1a0c92c24c0dc3e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3819644Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Derek Gonyeo <dgonyeo@google.com>
Cr-Commit-Position: refs/heads/main@{#82656}