Add additional tests for Proxy get and has property.

Bug: v8:6560, v8:6557
Change-Id: I56360c230b03a16425f4068d8023f90b3164eebb
Reviewed-on: https://chromium-review.googlesource.com/607889
Commit-Queue: Maya Lekova <mslekova@google.com>
Reviewed-by: Franziska Hinkelmann <franzih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47290}