[Editor] Move setting window.uiManager back to the test code

In PR #18574 setting `window.uiManager` was moved into the `src` folder
to avoid intermittent integration test failures because at the time we
lacked a way to register event listeners early (before PDF.js loads).
However, in PR #18617 this functionality got introduced, so we can now
use the new way of setting up the event bus in the tests to move this
back to the `test` folder again and to reduce the amount of test-only
code in the main codebase as discussed in PR #18574.

Partially reverts e037c57.

src/display/editor/tools.js

@@ -806,7 +806,6 @@ class AnnotationEditorUIManager {
     this.isShiftKeyDown = false;
 
     if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
-      window.uiManager = this;
       Object.defineProperty(this, "reset", {
         value: () => {
           this.selectAll();

test/integration/highlight_editor_spec.mjs

@@ -990,7 +990,13 @@ describe("Highlight Editor", () => {
         "tracemonkey.pdf",
         ".annotationEditorLayer",
         null,
-        null,
+        {
+          eventBusSetup: eventBus => {
+            eventBus.on("annotationeditoruimanager", ({ uiManager }) => {
+              window.uiManager = uiManager;
+            });
+          },
+        },
         {
           highlightEditorColors: "red=#AB0000",
           supportsCaretBrowsingMode: true,