A JSObject's own properties were always printed as if all were stored
in the 'properties' backing store, even if some of them were stored in
the descriptor array and/or in-object. This CL tries to make the output
a bit clearer.

Change-Id: I03d05bdd530cc4c534c945aa08bad20edc3bbcd7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2466119
Auto-Submit: Georg Neis <neis@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70475}