In https://crrev.com/c/2842128, a concern was raised that using
`V8InspectorSession::createCommandLineAPI` directly would not cache the command line
API definitions and V8 could expose a higher level API for this use
case. This CL exposes `InjectedScript::ContextScope` via V8InspectorSession.
If this approach is approved, V8InspectorSession::createCommandLineAPI
could be removed.

Example usage: https://crrev.com/c/2858964

Bug: chromium:1200705
Change-Id: Ib9fcadcb9bbd75c08f0122b0e4ee61e2874c4f8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2857640
Commit-Queue: Alex Rudenko <alexrudenko@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74289}