Add SharedLibraryInfo#isNative to @TestApi surface.

The method is used in ClasspathDeviceTest to filter out native .so
files, as it only cares about java classes.

Bug: 189347015
Bug: 187823488
Test: m
Change-Id: Id4d41ddef1cddbecd7f7028e28da4040cdfd5c26

core/api/test-current.txt

@@ -829,6 +829,7 @@ package android.content.pm {
 
   public final class SharedLibraryInfo implements android.os.Parcelable {
     method @NonNull public java.util.List<java.lang.String> getAllCodePaths();
+    method public boolean isNative();
   }
 
   public final class ShortcutInfo implements android.os.Parcelable {

core/java/android/content/pm/SharedLibraryInfo.java

@@ -147,6 +147,7 @@ public final class SharedLibraryInfo implements Parcelable {
      *
      * @hide
      */
+    @TestApi
     public boolean isNative() {
         return mIsNative;
     }