Support minimum to open user settings to a particular tab

Tabs now have IDs, and we use those IDs to open things. This doesn't do any conversion to typescript, and doesn't add the same feature to the room settings out of concern for the size of diff.

src/dispatcher/actions.ts

@@ -36,6 +36,7 @@ export enum Action {
 
     /**
      * Open the user settings. No additional payload information required.
+     * Optionally can include an OpenToTabPayload.
      */
     ViewUserSettings = "view_user_settings",
 

src/dispatcher/payloads/OpenToTabPayload.ts

@@ -0,0 +1,27 @@
+/*
+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 { ActionPayload } from "../payloads";
+import { Action } from "../actions";
+
+export interface OpenToTabPayload extends ActionPayload {
+    action: Action.ViewUserSettings | string, // TODO: Add room settings action
+
+    /**
+     * The tab ID to open in the settings view to start, if possible.
+     */
+    initialTabId?: string;
+}