Restore public visibility of onRefreshRateSettingsChanged

Bug:b/272803550
Test: atest DisplayModeDirectorTest

Public visibility was changed to package private in ag/21465168
test results: http://ab/I15700010138815406

Change-Id: Ie1f7af2d49f9e2aab70478f4e59ba43746c48036

services/core/java/com/android/server/display/mode/DisplayModeDirector.java

@@ -2088,7 +2088,7 @@ public class DisplayModeDirector {
         }
 
         @VisibleForTesting
-        void onRefreshRateSettingChangedLocked(float min, float max) {
+        public void onRefreshRateSettingChangedLocked(float min, float max) {
             boolean changeable = (max - min > 1f && max > 60f);
             if (mRefreshRateChangeable != changeable) {
                 mRefreshRateChangeable = changeable;