Update icon tint color when the user toggles Dark theme

- Reload theme in slice provider when Dark theme mode changes for slices
- Reload theme in onCreate of Panel activity for its non-slice header
- Remove applyTheme from individual slices

Test: robotest
Fixes: 153700819
Change-Id: I40a7d2817c4b9100d7b2f2962a69c8a9ce6f7906

src/com/android/settings/wifi/slice/WifiSlice.java

@@ -86,9 +86,6 @@ public class WifiSlice implements CustomSliceable {
 
     @Override
     public Slice getSlice() {
-        // Reload theme for switching dark mode on/off
-        mContext.getTheme().applyStyle(R.style.Theme_Settings_Home, true /* force */);
-
         final boolean isWifiEnabled = isWifiEnabled();
         ListBuilder listBuilder = getListBuilder(isWifiEnabled, null /* accessPoint */);
         if (!isWifiEnabled) {