Display existing reactions below the message

This displays the existing reactions a message has from all users below the
message.

Since we don't currently have an API to actually get these events yet,
adds a temporary hook that looks for a specific message to inject some sample
data. This helps build out the UI for now and can be removed once it exists.

Fixes https://github.com/vector-im/riot-web/issues/9573

src/components/views/rooms/EventTile.js

@@ -622,6 +622,14 @@ module.exports = withMatrixClient(React.createClass({
                 <ToolTipButton helpText={keyRequestHelpText} />
             </div> : null;
 
+        let reactions;
+        if (SettingsStore.isFeatureEnabled("feature_reactions")) {
+            const ReactionsRow = sdk.getComponent('messages.ReactionsRow');
+            reactions = <ReactionsRow
+                mxEvent={this.props.mxEvent}
+            />;
+        }
+
         switch (this.props.tileShape) {
             case 'notif': {
                 const EmojiText = sdk.getComponent('elements.EmojiText');
@@ -734,6 +742,7 @@ module.exports = withMatrixClient(React.createClass({
                                            showUrlPreview={this.props.showUrlPreview}
                                            onHeightChanged={this.props.onHeightChanged} />
                             { keyRequestInfo }
+                            { reactions }
                             { actionBar }
                         </div>
                         {