Add an intent for launching mobile network list

In various cases when a user has rebooted their device to enable DSDS
mode, the eSIM manager app needs to be able to post a notification that
on tapping will lead the user to the list of configured SIMs (mobile
networks) so that they can they manage things like which one is the
default for calls, SMS, and data.

Bug: 129281152
Test: 'adb shell am start -a android.settings.MOBILE_NETWORK_LIST'
should launch the list of mobile networks available on the device

Change-Id: Ie94d937c803fb5ade09084f2c994cfff888d8aa7

src/com/android/settings/Settings.java

@@ -162,6 +162,7 @@ public class Settings extends SettingsActivity {
     public static class AdvancedConnectedDeviceActivity extends SettingsActivity { /* empty */ }
     public static class BluetoothDeviceDetailActivity extends SettingsActivity { /* empty */ }
     public static class WifiCallingDisclaimerActivity extends SettingsActivity { /* empty */ }
+    public static class MobileNetworkListActivity extends SettingsActivity {}
 
     // Top level categories for new IA
     public static class NetworkDashboardActivity extends SettingsActivity {}