Change the getVisibleElements helper function to take a parameter object

Given the number of parameters, and the fact that many of them are booleans, the call-sites are no longer particularly easy to read and understand. Furthermore, this slightly improves the formatting of the JSDoc-comment, since it needed updating as part of these changes anyway.

Finally, this removes an unnecessary `numViews === 0` check from `getVisibleElements`, since that should be *very* rare and more importantly that the `binarySearchFirstItem` function already has a fast-path for that particular case.

web/pdf_thumbnail_viewer.js

@@ -81,7 +81,10 @@ class PDFThumbnailViewer {
    * @private
    */
   _getVisibleThumbs() {
-    return getVisibleElements(this.container, this._thumbnails);
+    return getVisibleElements({
+      scrollEl: this.container,
+      views: this._thumbnails,
+    });
   }
 
   scrollThumbnailIntoView(pageNumber) {