[Editor] Improve a11y for newly added element (#15109)

- In the annotationEditorLayer, reorder the editors in the DOM according
  the position of the elements on the screen;
- add an aria-owns attribute on the "nearest" element in the text layer
  which points to the added editor.

src/display/display_utils.js

@@ -601,7 +601,40 @@ function getColorValues(colors) {
   span.remove();
 }
 
+/**
+ * Use binary search to find the index of the first item in a given array which
+ * passes a given condition. The items are expected to be sorted in the sense
+ * that if the condition is true for one item in the array, then it is also true
+ * for all following items.
+ *
+ * @returns {number} Index of the first array element to pass the test,
+ *                   or |items.length| if no such element exists.
+ */
+function binarySearchFirstItem(items, condition, start = 0) {
+  let minIndex = start;
+  let maxIndex = items.length - 1;
+
+  if (maxIndex < 0 || !condition(items[maxIndex])) {
+    return items.length;
+  }
+  if (condition(items[minIndex])) {
+    return minIndex;
+  }
+
+  while (minIndex < maxIndex) {
+    const currentIndex = (minIndex + maxIndex) >> 1;
+    const currentItem = items[currentIndex];
+    if (condition(currentItem)) {
+      maxIndex = currentIndex;
+    } else {
+      minIndex = currentIndex + 1;
+    }
+  }
+  return minIndex; /* === maxIndex */
+}
+
 export {
+  binarySearchFirstItem,
   deprecated,
   DOMCanvasFactory,
   DOMCMapReaderFactory,