Some operations require an immediate argument that represents a heap
type. This CL introduces a class to represent it and uses it where
appropriate. Also, the redundant TypeIndexImmediate is removed.

Bug: v8:7748
Change-Id: Ib4b1d50764a79f5dd3240688f8165c39745eaad8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2260874
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68522}