Use TestUtil.getPublicMethods instead of getDeclaredMethods

JaCoCo introduces private synthetic methods (even on interfaces) which
have to be skipped when checking that a 'forwarding' implementation does
forward everything. Instead we can use the existing `getPublicMethods()`
method which implicitly skips these (since they're private).

PiperOrigin-RevId: 533130932
(cherry picked from commit 620b9e1540)

libraries/common/src/test/java/androidx/media3/common/SimpleBasePlayerTest.java

@@ -65,7 +65,7 @@ public class SimpleBasePlayerTest {
 
   @Test
   public void allPlayerInterfaceMethods_declaredFinal() throws Exception {
-    for (Method method : Player.class.getDeclaredMethods()) {
+    for (Method method : TestUtil.getPublicMethods(Player.class)) {
       assertThat(
               SimpleBasePlayer.class
                       .getMethod(method.getName(), method.getParameterTypes())