Move binarySearchFirstItem back to the web/-folder (PR 15237 follow-up)

This was moved into the `src/display/`-folder in PR 15110, for the initial editor-a11y patch. However, with the changes in PR 15237 we're again only using `binarySearchFirstItem` in the `web/`-folder and it thus seem reasonable to move it back there.
The primary reason for moving it back is that `binarySearchFirstItem` is currently exposed in the public API, and we always want to avoid that unless it's either PDF-related functionality or code that simply must be shared between the `src/`- and `web/`-folders. In this case, `binarySearchFirstItem` is a general helper function that doesn't really satisfy either of those alternatives.

web/pdf_find_controller.js

@@ -17,9 +17,9 @@
 /** @typedef {import("./event_utils").EventBus} EventBus */
 /** @typedef {import("./interfaces").IPDFLinkService} IPDFLinkService */
 
-import { binarySearchFirstItem, createPromiseCapability } from "pdfjs-lib";
+import { binarySearchFirstItem, scrollIntoView } from "./ui_utils.js";
+import { createPromiseCapability } from "pdfjs-lib";
 import { getCharacterType } from "./pdf_find_utils.js";
-import { scrollIntoView } from "./ui_utils.js";
 
 const FindState = {
   FOUND: 0,

web/text_accessibility.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import { binarySearchFirstItem } from "pdfjs-lib";
+import { binarySearchFirstItem } from "./ui_utils.js";
 
 /**
  * This class aims to provide some methods:

web/ui_utils.js

@@ -13,8 +13,6 @@
  * limitations under the License.
  */
 
-import { binarySearchFirstItem } from "pdfjs-lib";
-
 const DEFAULT_SCALE_VALUE = "auto";
 const DEFAULT_SCALE = 1.0;
 const DEFAULT_SCALE_DELTA = 1.1;
@@ -226,6 +224,38 @@ function removeNullCharacters(str, replaceInvisible = false) {
   return str.replace(NullCharactersRegExp, "");
 }
 
+/**
+ * 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 */
+}
+
 /**
  *  Approximates float number as a fraction using Farey sequence (max order
  *  of 8).
@@ -813,6 +843,7 @@ export {
   approximateFraction,
   AutoPrintRegExp,
   backtrackBeforeAllVisibleElements, // only exported for testing
+  binarySearchFirstItem,
   DEFAULT_SCALE,
   DEFAULT_SCALE_DELTA,
   DEFAULT_SCALE_VALUE,