Count and display invalid fields in toast. (#10249)

apps/browser/src/_locales/en/messages.json

@@ -2949,6 +2949,18 @@
       }
     }
   },
+  "singleFieldNeedsAttention": {
+    "message": "1 field needs your attention."
+  },
+  "multipleFieldsNeedAttention": {
+    "message": "$COUNT$ fields need your attention.",
+    "placeholders": {
+      "count": {
+        "content": "$1",
+        "example": "2"
+      }
+    }
+  },
   "selectPlaceholder": {
     "message": "-- Select --"
   },