Guest mode UX flow updates to user settings

- Add option in user settings to enable/disable ephemeral
  mode for guest user
- Update user settings to show exit guest and reset guest preferences
- Update user settings to show guest related preferences grouped together

Bug: 214031645, 175795666
Screenshots: go/ephemeral-guest-b-214031645-ux
Test: Manual test on sunfish, atest SystemUITests, atest SettingsRoboTests

Relands ag/16544951 after fixing post submit issues

Revert "Revert "Guest mode UX flow updates to user settings""

This reverts commit ed45e8c56a.

Change-Id: I54583f9021171ae523ff40d4f63835f1cb486e35

src/com/android/settings/users/UserDialogs.java

@@ -189,7 +189,7 @@ public final class UserDialogs {
             DialogInterface.OnClickListener onConfirmListener) {
         return new AlertDialog.Builder(context)
                 .setTitle(com.android.settingslib.R.string.guest_reset_guest_dialog_title)
-                .setMessage(R.string.user_exit_guest_confirm_message)
+                .setMessage(com.android.settingslib.R.string.guest_exit_dialog_message)
                 .setPositiveButton(
                         com.android.settingslib.R.string.guest_reset_guest_confirm_button,
                         onConfirmListener)