Do not leak handles to the outer scopes from inspector methods.
Add `SealHandleScope`s to the tests and the d8 binding, and
`HandleScope`s in the places in the inspector source where
handles are actually used.

Change-Id: I80b1bb0ccc4778b32e9198513f63d5c0652c8f59
Reviewed-on: https://chromium-review.googlesource.com/c/1484304Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59812}