Improve type definitions for the viewer

This commit improves compatibility of the viewer code with TypeScript by including missing type imports/definitions and correcting existing ones

web/pdf_cursor_tools.js

@@ -13,6 +13,8 @@
  * limitations under the License.
  */
 
+/** @typedef {import("./event_utils.js").EventBus} EventBus */
+
 import { AnnotationEditorType, shadow } from "pdfjs-lib";
 import { CursorTool, PresentationModeState } from "./ui_utils.js";
 import { GrabToPan } from "./grab_to_pan.js";