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/components/views/elements/Pill.js

@@ -26,6 +26,7 @@ import {MatrixClientPeg} from '../../../MatrixClientPeg';
 import FlairStore from "../../../stores/FlairStore";
 import {getPrimaryPermalinkEntity} from "../../../utils/permalinks/Permalinks";
 import MatrixClientContext from "../../../contexts/MatrixClientContext";
+import {Action} from "../../../dispatcher/actions";
 
 // For URLs of matrix.to links in the timeline which have been reformatted by
 // HttpUtils transformTags to relative links. This excludes event URLs (with `[^\/]*`)
@@ -191,7 +192,7 @@ const Pill = createReactClass({
 
     onUserPillClicked: function() {
         dis.dispatch({
-            action: 'view_user',
+            action: Action.ViewUser,
             member: this.state.member,
         });
     },