[GENERIC viewer] Try to improve a11y, for search results, in the find…

…bar (issue 14525)

*Please note:* I don't really know anything about a11y, hence it's possible that this patch either doesn't work correctly or at least isn't a complete solution.

Based on skimming through the two MDN articles linked below, it seems that tagging the `findMsg` and `findResultsCount` spans accordingly could be a solution to notify a11y software about search results.

 - https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/status_role
 - https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_status_role

web/viewer.html

@@ -116,7 +116,7 @@
       <div id="mainContainer">
         <div class="findbar hidden doorHanger" id="findbar">
           <div id="findbarInputContainer">
-            <input id="findInput" class="toolbarField" title="Find" placeholder="Find in document…" tabindex="91" data-l10n-id="find_input">
+            <input id="findInput" class="toolbarField" title="Find" placeholder="Find in document…" tabindex="91" data-l10n-id="find_input" aria-controls="findMsg findResultsCount">
             <div class="splitToolbarButton">
               <button id="findPrevious" class="toolbarButton findPrevious" title="Find the previous occurrence of the phrase" tabindex="92" data-l10n-id="find_previous">
                 <span data-l10n-id="find_previous_label">Previous</span>
@@ -142,10 +142,10 @@
           </div>
 
           <div class="findbarMessageContainer">
-            <span id="findResultsCount" class="toolbarLabel"></span>
+            <span id="findResultsCount" class="toolbarLabel" role="status"></span>
           </div>
           <div class="findbarMessageContainer">
-            <span id="findMsg" class="toolbarLabel"></span>
+            <span id="findMsg" class="toolbarLabel" role="status"></span>
           </div>
         </div>  <!-- findbar -->