Expose getPreferKeepClearForFocusDelay as TestApi

This allows tests to check the behavior of automatically reporting the
focused View as a keep clear area.

Test: atest KeepClearRectsTests
Bug: 218494300
Change-Id: I602406572a540c4b5f77164efab28376faec2701

core/api/test-current.txt

@@ -2876,6 +2876,7 @@ package android.view {
     method public static int getHoverTooltipHideTimeout();
     method public static int getHoverTooltipShowTimeout();
     method public static int getLongPressTooltipHideTimeout();
+    method public int getPreferKeepClearForFocusDelay();
   }
 
   public class ViewDebug {

core/java/android/view/ViewConfiguration.java

@@ -1104,6 +1104,7 @@ public class ViewConfiguration {
      *         clear, or -1 if Views should not set themselves as preferred to keep clear.
      * @hide
      */
+    @TestApi
     public int getPreferKeepClearForFocusDelay() {
         return mPreferKeepClearForFocusDelay;
     }