extensions: Add more stub behavior for chrome.tabs on desktop Android

Add a stub for chrome.tabs.query() that just returns the ID of the
currently active tab.

Add a stub implementation of ExtensionTabUtil::CreateTabObject() that
returns the ID and index of the tab.

This gets us closer to being able to demonstrate real extensions from
the web store. (For example, "Simply Dark" queries the current tab
to get its ID, then uses that ID to send a message to JS in the tab.)

Bug: 371432155
Change-Id: I62ddc2bfa10cab36bac5b33d4cc3963562e5ecd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6594245
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Shuhei Takahashi <nya@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1466280}