compose: Configure button to generate video chat url on tap

This commit adds function and then Configure to
generate jitsi unique meeting ID and to fetch
video chat url as per realmVideoChatProvider

Author: MritunjayTiwari14

lib/widgets/compose_box.dart

@@ -1040,7 +1040,33 @@ class _AttachVideoChatUrlButton extends StatelessWidget {
   final ComposeBoxController controller;
   final bool enabled;
 
+  static const int jitsi = 1;
+  static const int zoom = 2; //TODO: Add other supported video chat providers
+
+  String _generateJitsiUrl(String serverUrl, String visibleText) {
+    final id = List.generate(15, (_) => Random.secure().nextInt(10)).join();
+    return inlineLink(visibleText, '$serverUrl/$id#config.startWithVideoMuted=false');
+  }
+
+  String? _getMeetingUrl(ZulipLocalizations zulipLocalization, int? provider, String? jitsiServerUrl) {
+    final visibleText = zulipLocalization.composeBoxUploadedVideoCallUrl;
+
+    switch (provider) {
+      case 0: return null; //TODO: Implement feedback no video chat provider is setup
+      case jitsi: return jitsiServerUrl == null ? null :_generateJitsiUrl(jitsiServerUrl, visibleText);
+      case zoom: return inlineLink(visibleText,
+        'https://zoom.us/start/meeting');
+      default: return null;
+    }
+  }
+
   void _handlePress(BuildContext context) {
+    final store = PerAccountStoreWidget.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
+
+    final placeholder = _getMeetingUrl(zulipLocalizations,
+        store.realmVideoChatProvider, store.jitsiServerUrl);
+    if (placeholder == null) return;
   }
 
   @override