Reland "app_list: Make search result actions views keyboard accessible"

This is a reland of d4425b7de06d5904f325b7e25ac4155f93a01c51

TBR=xiyuan@chromium.org

Original change's description:
> app_list: Make search result actions views keyboard accessible
>
> Summary of changes:
> *   Added methods for keeping track of currently selected action, and
>     for moving the selection to SearchResultActionsView
> *   Added SearchResultActionsViewDelegate::
>     OnSearchResultActionsUnSelected so the result view can handle the
>     case where actions are un selected - primarily, it sends out a
>     a11y notification that the default action (that activates the
>     search result) is selected again
> *   Renamed SearchResultBaseView::SetBackgroundHighlighted to
>     SetSelected, and added logic for setting initial selected result
>     action, or clearing action selection. (the latter is protected by
>     SearchBoxSelectionEnabled feature).
> *   Added SearchResultBaseView::SelectNextResultAction - used by result
>     selection controller to move the action selection if needed.
>     *    Note: The SearchResultBaseView implementations are expected
>          to call newly added set_actions_view to register their result
>          actions - otherwise this method will be no-op
> *   ResultSelectionController::ResetSelection avoids clearing and
>     setting selection again if the view that should be selected is
>     already selected
>
> BUG=986382
>
> Change-Id: I9932e9c44abe546b71fbcbf1488c9ac076ae5c84
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1713223
> Commit-Queue: Toni Baržić <tbarzic@chromium.org>
> Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#680507}

Bug: 986382
Change-Id: Ie15d7bf6ac7ff82597e876619d451ee2d9466840
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726411
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682777}