Add optional mobile guide toast

This adds an optional toast which Element deployments can enable to nudge users
towards the mobile apps once they are inside the app.

Part of https://github.com/vector-im/element-web/issues/16283

src/components/structures/MatrixChat.tsx

@@ -81,6 +81,7 @@ import ThreepidInviteStore, { IThreepidInvite, IThreepidInviteWireFormat } from
 import {UIFeature} from "../../settings/UIFeature";
 import { CommunityPrototypeStore } from "../../stores/CommunityPrototypeStore";
 import DialPadModal from "../views/voip/DialPadModal";
+import { showToast as showMobileGuideToast } from '../../toasts/MobileGuideToast';
 
 /** constants for MatrixChat.state.view */
 export enum Views {
@@ -1186,6 +1187,11 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         ) {
             showAnalyticsToast(this.props.config.piwik?.policyUrl);
         }
+        if (SdkConfig.get().mobileGuideToast) {
+            // The toast contains further logic to detect mobile platforms,
+            // check if it has been dismissed before, etc.
+            showMobileGuideToast();
+        }
     }
 
     private showScreenAfterLogin() {