Convert view_user dispatch to prove the conversion works

This is a relatively obvious dispatch action that doesn't require a lot of complicated type definitions, so should be a good candidate to prove the thing works. If for some reason the thing stops working, we've done something wrong.

This also adds a bit of generic types to the dispatch call so we don't confuse the tsx parser by using `dis.dispatch(<ViewUserPayload>{...})` as it thinks that's supposed to be a component. We still get type safety, and the thing remains happy with the generics approach.

src/dispatcher/payloads/ViewUserPayload.ts

@@ -0,0 +1,29 @@
+/*
+Copyright 2020 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 { RoomMember } from "matrix-js-sdk/src/models/room-member";
+import { ActionPayload } from "../payloads";
+import { Action } from "../actions";
+
+export interface ViewUserPayload extends ActionPayload {
+    action: Action.ViewUser,
+
+    /**
+     * The member to view. May be null or falsy to indicate that no member
+     * should be shown (hide whichever relevant components).
+     */
+    member?: RoomMember;
+}