icons: Add message_checked icon, from Figma

Figma doesn't specify this icon explicitly. Based on discussions in PR #1274
(#1274 (comment)),
we chose this icon for consistency with the "Mark as read" option on web.

reference: https://www.figma.com/design/1JTNtYo9memgW7vV6d0ygq/Zulip-Mobile?node-id=3512-7&t=iwirdCVutQls9R0A-4

Author: chimnayajith

assets/icons/ZulipIcons.ttf

@@ -93,44 +93,47 @@ abstract final class ZulipIcons {
   /// The Zulip custom icon "menu".
   static const IconData menu = IconData(0xf117, fontFamily: "Zulip Icons");
 
+  /// The Zulip custom icon "message_checked".
+  static const IconData message_checked = IconData(0xf118, fontFamily: "Zulip Icons");
+
   /// The Zulip custom icon "message_feed".
-  static const IconData message_feed = IconData(0xf118, fontFamily: "Zulip Icons");
+  static const IconData message_feed = IconData(0xf119, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "mute".
-  static const IconData mute = IconData(0xf119, fontFamily: "Zulip Icons");
+  static const IconData mute = IconData(0xf11a, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "read_receipts".
-  static const IconData read_receipts = IconData(0xf11a, fontFamily: "Zulip Icons");
+  static const IconData read_receipts = IconData(0xf11b, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "send".
-  static const IconData send = IconData(0xf11b, fontFamily: "Zulip Icons");
+  static const IconData send = IconData(0xf11c, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "share".
-  static const IconData share = IconData(0xf11c, fontFamily: "Zulip Icons");
+  static const IconData share = IconData(0xf11d, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "share_ios".
-  static const IconData share_ios = IconData(0xf11d, fontFamily: "Zulip Icons");
+  static const IconData share_ios = IconData(0xf11e, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "smile".
-  static const IconData smile = IconData(0xf11e, fontFamily: "Zulip Icons");
+  static const IconData smile = IconData(0xf11f, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "star".
-  static const IconData star = IconData(0xf11f, fontFamily: "Zulip Icons");
+  static const IconData star = IconData(0xf120, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "star_filled".
-  static const IconData star_filled = IconData(0xf120, fontFamily: "Zulip Icons");
+  static const IconData star_filled = IconData(0xf121, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "three_person".
-  static const IconData three_person = IconData(0xf121, fontFamily: "Zulip Icons");
+  static const IconData three_person = IconData(0xf122, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "topic".
-  static const IconData topic = IconData(0xf122, fontFamily: "Zulip Icons");
+  static const IconData topic = IconData(0xf123, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "unmute".
-  static const IconData unmute = IconData(0xf123, fontFamily: "Zulip Icons");
+  static const IconData unmute = IconData(0xf124, fontFamily: "Zulip Icons");
 
   /// The Zulip custom icon "user".
-  static const IconData user = IconData(0xf124, fontFamily: "Zulip Icons");
+  static const IconData user = IconData(0xf125, fontFamily: "Zulip Icons");
 
   // END GENERATED ICON DATA
 }