Update JavaDoc for DragEvent.getLocalState

Explicitly state that "local state" is local to the window
which has started the drag operation.

Bug: 31372686
Change-Id: Idbea7586c4e74097362067fa90390b97744181bb

core/java/android/view/DragEvent.java

@@ -377,6 +377,10 @@ public class DragEvent implements Parcelable {
      * The object is intended to provide local information about the drag and drop operation. For
      * example, it can indicate whether the drag and drop operation is a copy or a move.
      * <p>
+     * The local state is available only to views in the activity which has started the drag
+     * operation. In all other activities this method will return null
+     * </p>
+     * <p>
      *  This method returns valid data for all event actions except for {@link #ACTION_DRAG_ENDED}.
      * </p>
      * @return The local state object sent to the system by startDrag().

core/java/android/view/View.java

@@ -20524,8 +20524,10 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
      * @param shadowBuilder A {@link android.view.View.DragShadowBuilder} object for building the
      * drag shadow.
      * @param myLocalState An {@link java.lang.Object} containing local data about the drag and
-     * drop operation. This Object is put into every DragEvent object sent by the system during the
-     * current drag.
+     * drop operation. When dispatching drag events to views in the same activity this object
+     * will be available through {@link android.view.DragEvent#getLocalState()}. Views in other
+     * activities will not have access to this data ({@link android.view.DragEvent#getLocalState()}
+     * will return null).
      * <p>
      * myLocalState is a lightweight mechanism for the sending information from the dragged View
      * to the target Views. For example, it can contain flags that differentiate between a