Restrict WiFi network connection

- Use StandardWifiEntry#canConnect() to determine if the network should
  be disabled or not.

- Use StandardWifiEntry#getSummary() to retrieve the restriction message.

- Disabled WiFi network if it cannot connect.

- If WiFi network is connected or saved network, leave it enabled to
disconnect or configure.

- See the result screenshot in b/203168943#comment11

Bug: 203168938
Bug: 203168943
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=LongPressWifiEntryPreferenceTest
make RunSettingsRoboTests ROBOTEST_FILTER=NetworkProviderSettingsTest

Change-Id: I04aafaa5b383598a0f87eea15d06b38bbc662b9e

src/com/android/settings/wifi/LongPressWifiEntryPreference.java

@@ -17,6 +17,7 @@ package com.android.settings.wifi;
 
 import android.content.Context;
 
+import androidx.annotation.VisibleForTesting;
 import androidx.fragment.app.Fragment;
 import androidx.preference.PreferenceViewHolder;
 
@@ -43,4 +44,23 @@ public class LongPressWifiEntryPreference extends WifiEntryPreference {
             view.itemView.setLongClickable(true);
         }
     }
+
+    @Override
+    public void refresh() {
+        super.refresh();
+        setEnabled(shouldEnabled());
+    }
+
+    @VisibleForTesting
+    boolean shouldEnabled() {
+        WifiEntry wifiEntry = getWifiEntry();
+        if (wifiEntry == null) return false;
+
+        boolean enabled = wifiEntry.canConnect();
+        // If Wi-Fi is connected or saved network, leave it enabled to disconnect or configure.
+        if (!enabled && (wifiEntry.canDisconnect() || wifiEntry.isSaved())) {
+            enabled = true;
+        }
+        return enabled;
+    }
 }