Add icons for thread badges

Riot/Assets/Images.xcassets/Room/Threads/threads_icon_red_dot.imageset/Contents.json

@@ -0,0 +1,15 @@
+{
+  "images" : [
+    {
+      "filename" : "light-and-dark-theme-mentions.svg",
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  },
+  "properties" : {
+    "template-rendering-intent" : "original"
+  }
+}

Riot/Assets/Images.xcassets/Room/Threads/threads_icon_red_dot.imageset/light-and-dark-theme-mentions.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="28" height="28" fill="none" viewBox="0 0 28 28"><circle cx="23" cy="5" r="5" fill="#FF5B55"/><path fill="#0DBD8B" fill-rule="evenodd" d="M16.07 6A7.004 7.004 0 0 0 22 11.93V21a3 3 0 0 1-3 3H7.667a1 1 0 0 0-.6.2L3.6 26.8A1 1 0 0 1 2 26V9a3 3 0 0 1 3-3h11.07ZM6 12a1 1 0 1 0 0 2h12a1 1 0 1 0 0-2H6Zm-1 5a1 1 0 0 1 1-1h6a1 1 0 1 1 0 2H6a1 1 0 0 1-1-1Z" clip-rule="evenodd"/></svg>