Refactor getting allowlist set from feature provider.

(1) Use Set<CharSequence> for all the allowlists.
(2) The contains() method of Set<CharSequence> also works for String. No
    need an extra contains() util function.

Bug: 262802531
Fix: 262802531
Test: presubmit
Change-Id: Ib2aaf9a3b8db4618a8c46f138e8d35f15b77c104

src/com/android/settings/fuelgauge/PowerUsageFeatureProvider.java

@@ -146,9 +146,9 @@ public interface PowerUsageFeatureProvider {
     Set<CharSequence> getHideBackgroundUsageTimeSet(Context context);
 
     /**
-     * Returns package names for hiding application in the usage screen.
+     * Returns {@link Set} for hiding application package names in the usage screen.
      */
-    CharSequence[] getHideApplicationEntries(Context context);
+    Set<CharSequence> getHideApplicationSet(Context context);
 
     /**
      * Returns {@link Set} for ignoring task root class names for screen on time.