Clarify what ignoring battery optimizations means.

Add some more definition to what it means to be on the power allowlist.

Bug: 173547576
Test: N/A
Change-Id: I6c6bd3248dc39877e560656e787ef02adf7d279f

core/java/android/os/PowerManager.java

@@ -2107,6 +2107,8 @@ public final class PowerManager {
      * Return whether the given application package name is on the device's power allowlist.
      * Apps can be placed on the allowlist through the settings UI invoked by
      * {@link android.provider.Settings#ACTION_IGNORE_BATTERY_OPTIMIZATION_SETTINGS}.
+     * <p>Being on the power allowlist means that the system will not apply most power saving
+     * features to the app. Guardrails for extreme cases may still be applied.
      */
     public boolean isIgnoringBatteryOptimizations(String packageName) {
         return getPowerWhitelistManager().isWhitelisted(packageName, true);