Mark JSPointerDispatcher and JSTouchDispatcher as open

The Java-to-Kotlin migration of these classes made them implicitly
final (Kotlin default), breaking downstream libraries that subclass
them (e.g. react-native-keyboard-controller's JSPointerDispatcherCompat).

Adding `open` restores the pre-migration extensibility.

Author: cortinico

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/JSPointerDispatcher.kt

@@ -28,7 +28,7 @@ import com.facebook.react.uimanager.events.PointerEventHelper.EVENT
  * onHoverEvent, onInterceptHoverEvent. It will correctly find the right view to handle the touch
  * and also dispatch the appropriate event to JS
  */
-public class JSPointerDispatcher(private val rootViewGroup: ViewGroup) {
+public open class JSPointerDispatcher(private val rootViewGroup: ViewGroup) {
 
   private var lastHitPathByPointerId: MutableMap<Int, List<ViewTarget>>? = null
   private var lastEventCoordinatesByPointerId: MutableMap<Int, FloatArray>? = null

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/JSTouchDispatcher.kt

@@ -25,7 +25,7 @@ import com.facebook.react.uimanager.events.TouchEventType
  * need to call handleTouchEvent from onTouchEvent and onInterceptTouchEvent. It will correctly find
  * the right view to handle the touch and also dispatch the appropriate event to JS
  */
-public class JSTouchDispatcher(private val viewGroup: ViewGroup) {
+public open class JSTouchDispatcher(private val viewGroup: ViewGroup) {
   private var targetTag = -1
   private val targetCoordinates = FloatArray(2)
   private var childIsHandlingNativeGesture = false