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/SlashCommands.tsx

@@ -41,6 +41,8 @@ import { parseFragment as parseHtml } from "parse5";
 import sendBugReport from "./rageshake/submit-rageshake";
 import SdkConfig from "./SdkConfig";
 import { ensureDMExists } from "./createRoom";
+import { ViewUserPayload } from "./dispatcher/payloads/ViewUserPayload";
+import { Action } from "./dispatcher/actions";
 
 // XXX: workaround for https://github.com/microsoft/TypeScript/issues/31816
 interface HTMLInputEvent extends Event {
@@ -943,8 +945,10 @@ export const Commands = [
             }
 
             const member = MatrixClientPeg.get().getRoom(roomId).getMember(userId);
-            dis.dispatch({
-                action: 'view_user',
+            dis.dispatch<ViewUserPayload>({
+                action: Action.ViewUser,
+                // XXX: We should be using a real member object and not assuming what the
+                // receiver wants.
                 member: member || {userId},
             });
             return success();