Extract v1 extensible events polls types out of the events-sdk (#3062)

* Extract v1 extensible events polls out of events-sdk

* Appease tsdoc?

* Appease naming standards

* Bring the tests over too

spec/unit/extensible_events_v1/ExtensibleEvent.spec.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2022 - 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { ExtensibleEventType, IPartialEvent } from "../../../src/@types/extensible_events";
+import { ExtensibleEvent } from "../../../src/extensible_events_v1/ExtensibleEvent";
+
+class MockEvent extends ExtensibleEvent<any> {
+    public constructor(wireEvent: IPartialEvent<any>) {
+        super(wireEvent);
+    }
+
+    public serialize(): IPartialEvent<object> {
+        throw new Error("Not implemented for tests");
+    }
+
+    public isEquivalentTo(primaryEventType: ExtensibleEventType): boolean {
+        throw new Error("Not implemented for tests");
+    }
+}
+
+describe("ExtensibleEvent", () => {
+    it("should expose the wire event directly", () => {
+        const input: IPartialEvent<any> = { type: "org.example.custom", content: { hello: "world" } };
+        const event = new MockEvent(input);
+        expect(event.wireFormat).toBe(input);
+        expect(event.wireContent).toBe(input.content);
+    });
+});