Fix visibility and editability of importance fields

- Block field should always be visible
- Locked by OEM: cannot block or change importance
- Locked by default app: cannot block, can change importance
- Locked by system app: cannot block, can change importance
- system app but blockable: can block, can change importance

Test: robotests
Fixes: 131248127
Change-Id: Ifa718c84573dd5125aefa4f672a79dc4f267d515

tests/robotests/src/com/android/settings/notification/LightsPreferenceControllerTest.java

@@ -159,11 +159,9 @@ public class LightsPreferenceControllerTest {
 
     @Test
     public void testUpdateState_notBlockable() {
-        String lockedId = "locked";
         NotificationBackend.AppRow appRow = new NotificationBackend.AppRow();
-        appRow.lockedChannelId = lockedId;
         NotificationChannel channel = mock(NotificationChannel.class);
-        when(channel.getId()).thenReturn(lockedId);
+        when(channel.isImportanceLockedByOEM()).thenReturn(true);
         mController.onResume(appRow, channel, null, null);
 
         Preference pref = new RestrictedSwitchPreference(mContext);