- set role="application" on toolbar and sidebar to force
screen readers to use focus mode in those areas since
reading mode is not applicable here and one should not have
to manually switch to focus mode
- made outline values visible to screen readers
- improved aria-live message announced during search navigation
to include the page number as well as the snippet of the
result
- added role="navigation" to start containers of epub ranges
so that screen readers indicate when one moves to a new page.
It also enabled navigation via d/shift-d for NVDA and r/shift-r
for JAWS to go to next/previous page as with PDFs.
- added a state variable a11yVirtualCursorTarget to record
which node the screen readers should place its virtual cursor
on next time the focus enters the reader.
It forces virtual cursor to be moved onto that node, as
opposed to landing in the beginning of the document.
It is currently used to make sure screen readers begin reading
the chapter/section selected in the outline, as well as to
place virtual cursor on the last search result. On scroll,
a11yVirtualCursorTarget is cleared to not interfere with
mouse navigation. To make sure that scroll events of document
that fire when outline is navigated don't clear the a11yVirtualCursorTarget
that was just set, we wait for scrolling to finish and do
not allow a11yVirtualCursorTarget to be cleared if it was added
within the last 0.5 second.

So that screen reader users land on the right page
after changing the page number in the input or via
buttons next to it. Once the input is changed,
Escape keypress re-focuses the reader and it will
focus an element at the top of the page for virtual
cursor to move.

Except for placeA11yVirtualCursor which has the logic
shared by all view types but it now fetches the node to
focus from the view.

- Update the target node to focus for in _updateViewStats
which triggers on every view scroll update. It allows
us to have one place where we record which page to
refocus, as opposed to doing it for every navigation
method
- To make sure our updates don't run too often and
are not cleared by the scroll listener right after
they are set, a11yWillPlaceVirtCursorOnTop runs
through a debounce which will set the node when
view updates are all finished.
- Removed timestamp of what the target was recorded
since it's irrelevant now
- Instead, added allowUpdates variable which will
not allow the node of _a11yVirtualCursorTarget to be
updated. It is needed for search results to not get
overriden by the a11yWillPlaceVirtCursorOnTop when
scrolling is done

Have pdfjs handle it

So that views can share it without keeping it in
the reader.js.

Also, clear the virtual cursor target on mousedown
instead of during scroll - it also fixes the issue of
focus jumping to focused element on click after
scroll after an outline entry is selected. But it
also allows us to avoid multiple processes fighting
to set or clear virtual cursor and reduce debounce timeout
as a result.

General refactoring to handle search result announcements
from top-level Reader. a11yAnnounceSearchMessage
adds readers currentSnippet and currentPageLabel from
findState result if provided. Those don't exist for pdfs yet.

Added currentSnippet and currentPageLabel to be included
in epub and snapshot search results, so those are announced.

More refactoring to avoid different event handlers fighting
over who gets to set _a11yVirtualCursorTarget. It will
just not be set by the navigation handler during search mode,
which allows us to remove extraneous .allowUpdates field.

Removed a11yHandleSearchResultUpdate from all views since
messages are handler in Reader and curtorTargets can now be just
set directly in findNext/findPrevious.

Added a11yWillPlaceVirtCursorOnSearchResult specifically for pdf-view
to update virtual cursor target, since findNext does not fire on
first result, so we call a11yWillPlaceVirtCursorOnSearchResult
when findState is updated.

Set aria-label on epub paragraphs directly

And use it to get localized page label for epub