This adds inference for general JSObjects to NativeContextInferrer in
the case when the object is going to be attributed to the shard context.

Bug: chromium:973627
Change-Id: I393e8dd16a1f8b615fb2f8dceb52f543bae33554
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1997133Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65736}