poll: Show UI feedback for poll vote delays

Improve PollWidget to give immediate feedback on vote actions,
updating the opacity of the specific poll option while the vote
is in progress.

Fixes: #1808

Author: MritunjayTiwari14

lib/widgets/poll.dart

@@ -20,6 +20,7 @@ class PollWidget extends StatefulWidget {
 }
 
 class _PollWidgetState extends State<PollWidget> {
+  final Map<String, bool> _loadingOptions = {};
   @override
   void initState() {
     super.initState();
@@ -43,30 +44,31 @@ class _PollWidgetState extends State<PollWidget> {
 
   void _modelChanged() {
     setState(() {
+      _loadingOptions.clear();
       // The actual state lives in the [Poll] model.
       // This method was called because that just changed.
     });
   }
 
   void _toggleVote(PollOption option) async {
-    final navigator = Navigator.of(context);
-
-    unawaited(showDialog(context: context,
-        barrierDismissible: false,
-        builder: (_) {
-        return Center(child: CircularProgressIndicator());
-      }
-    ));
-
     final store = PerAccountStoreWidget.of(context);
     final op = option.voters.contains(store.selfUserId)
       ? PollVoteOp.remove
       : PollVoteOp.add;
+
+    setState(() {
+      if(option.voters.contains(store.selfUserId)) {
+        option.voters.remove(store.selfUserId);
+      } else {
+        option.voters.add(store.selfUserId);
+      }
+
+      _loadingOptions[option.key] = true;
+    });
+
     await(sendSubmessage(store.connection, messageId: widget.messageId,
       submessageType: SubmessageType.widget,
       content: PollVoteEventSubmessage(key: option.key, op: op)));
-
-    navigator.pop();
   }
 
   @override
@@ -95,12 +97,14 @@ class _PollWidgetState extends State<PollWidget> {
         .join(', ');
 
       return Row(
-        crossAxisAlignment: CrossAxisAlignment.baseline,
+        crossAxisAlignment: CrossAxisAlignment.center,
         textBaseline: localizedTextBaseline(context),
         children: [
           GestureDetector(
             // TODO: Implement feedback when the user taps the button
-            onTap: () => _toggleVote(option),
+            onTap: () => _loadingOptions[option.key] ?? false
+                ? null
+                : _toggleVote(option),
             behavior: HitTestBehavior.translucent,
             child: ConstrainedBox(
               constraints: const BoxConstraints(minWidth: 44, minHeight: 44),
@@ -117,7 +121,9 @@ class _PollWidgetState extends State<PollWidget> {
                   // there are more than three digits).
                   padding: const EdgeInsets.symmetric(horizontal: 4),
                   decoration: BoxDecoration(
-                    color: theme.colorPollVoteCountBackground,
+                    color: _loadingOptions[option.key] ?? false
+                      ? theme.colorPollVoteCountBackground.withValues(alpha: 1.0)
+                      : theme.colorPollVoteCountBackground,
                     border: Border.all(color: theme.colorPollVoteCountBorder),
                     borderRadius: BorderRadius.circular(3)),
                   child: Center(