Bookmarks: Fix key handling regressions from Lit migration

(1) Fix issue with item and list handling the same key event, which led
    to them cancelling each other out with Lit vs Polymer timing, by
    not handling ctrl + space in the individual items.
(2) Fix related issue with the list key handler not always calling
    e.stopPropagation() synchronously (meaning it would not have an
    effect) by making the handler synchronous.
(3) Fix issue revealed by tests after fixing (2), where the document key
    handlers in app mistakenly lost the capture setting when migrating
    to EventTracker.

Also adding a regression test for (1).

Fixed: 415018776
Change-Id: I54f4289c85af1bdb85bcf14e2ebda31863437192
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6506365
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1455148}