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
Change-Id: I7cf205883f8250178ac24c67c74b9142ceb6c1f5

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

@@ -34,6 +34,7 @@ public class UserCapabilities {
     boolean mCanAddRestrictedProfile;
     boolean mIsAdmin;
     boolean mIsGuest;
+    boolean mIsEphemeral;
     boolean mUserSwitcherEnabled;
     boolean mCanAddGuest;
     boolean mDisallowAddUser;
@@ -56,6 +57,7 @@ public class UserCapabilities {
         final UserInfo myUserInfo = userManager.getUserInfo(UserHandle.myUserId());
         caps.mIsGuest = myUserInfo.isGuest();
         caps.mIsAdmin = myUserInfo.isAdmin();
+        caps.mIsEphemeral = myUserInfo.isEphemeral();
         DevicePolicyManager dpm = (DevicePolicyManager) context.getSystemService(
                 Context.DEVICE_POLICY_SERVICE);