The TraceTrait for JSMember is currently missing GetTraceDescriptor.
We missed it because we don't have proper tests for JSMember, but it
would fail to build if it was ever actually traced.

Bug: chromium:1056170
Change-Id: I45fd2c7c666e791f866813f762b488958f65f3cf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2460815Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70413}