Split method into ShouldRecordRelocSlot and ProcessRelocInfo.
ProcessRelocInfo can then be reused in the write barrier and in the
future for the OLD_TO_SHARED remembered set. SlotTypeForRelocInfoMode
got moved into ProcessRelocInfo.

In addition rename and document SlotTypes. This CL does not change
behavior.

Bug: v8:11708
Change-Id: Iff712e7e6f5d3a4da64510b67b604b9e04998361
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3400968Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78701}