Add ViewsSimplifiedFullscreenUI to the fieldtrial testing config on Mac

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
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         }
     ],
     "VarationsServiceControl": [
         {
             "group_name": "Interval_30min",
             "params": {
                 "fetch_period_min": "30"
             }
         }
     ],
+    "ViewsSimplifiedFullscreenUI": [
+        {
+            "enable_features": [
+                "ViewsSimplifiedFullscreenUI"
+            ],
+            "group_name": "Enabled"
+        }
+    ],
     "WebFontsIntervention": [
         {
             "group_name": "Enabled"
         }
     ],
     "WebRTC-LocalIPPermissionCheck": [
         {
             "group_name": "Enabled"
         }
     ],
     "WebRTC-PeerConnectionDTLS1.2": [
         {
             "group_name": "Enabled"
         }
     ]
 }