Add signal-support in the EventBus, and utilize it in the viewer (PR 17964 follow-up)

This mimics the `signal` option that's available for `addEventListener`, see [MDN](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#signal).

test/unit/event_utils_spec.js

@@ -143,6 +143,60 @@ describe("event_utils", function () {
       expect(onceCount).toEqual(1);
     });
 
+    it("dispatch event to handlers with/without 'signal' option, aborted *before* dispatch", function () {
+      const eventBus = new EventBus();
+      const ac = new AbortController();
+      let multipleCount = 0,
+        noneCount = 0;
+
+      eventBus.on("test", function () {
+        multipleCount++;
+      });
+      eventBus.on(
+        "test",
+        function () {
+          noneCount++;
+        },
+        { signal: ac.signal }
+      );
+
+      ac.abort();
+
+      eventBus.dispatch("test");
+      eventBus.dispatch("test");
+      eventBus.dispatch("test");
+
+      expect(multipleCount).toEqual(3);
+      expect(noneCount).toEqual(0);
+    });
+
+    it("dispatch event to handlers with/without 'signal' option, aborted *after* dispatch", function () {
+      const eventBus = new EventBus();
+      const ac = new AbortController();
+      let multipleCount = 0,
+        onceCount = 0;
+
+      eventBus.on("test", function () {
+        multipleCount++;
+      });
+      eventBus.on(
+        "test",
+        function () {
+          onceCount++;
+        },
+        { signal: ac.signal }
+      );
+
+      eventBus.dispatch("test");
+      ac.abort();
+
+      eventBus.dispatch("test");
+      eventBus.dispatch("test");
+
+      expect(multipleCount).toEqual(3);
+      expect(onceCount).toEqual(1);
+    });
+
     it("should not re-dispatch to DOM", async function () {
       if (isNodeJS) {
         pending("Document is not supported in Node.js.");