The files src/base/v8-fallthrough.h, src/heap/cppgc/globals.h and
src/heap/cppgc/visitor.h were missing from BUILD.gn. This adds them and
modified the dependencies to make them visible.

Bug: v8:7330
Change-Id: I2be336697d50dd5623c0fc22637c8ab4b184ae39
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3028384Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75735}