Bump the memory size limit of memory64 memories from 4GB to 16GB. Tests
are added for larger sizes (5GB, 16GB).

Drive-by: Improve two decoder errors to properly include the unit,
  tested by the new tests.

R=jkummerow@chromium.org

Bug: v8:10949
Change-Id: I99dfc216b9213838784214c0b65ba863831d5884
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3789507Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82105}