ObjPtr<>-ify ClassLinker::FindClass(), fix 1 stale reference use.

Thread::CreateAnnotatedStackTrace() was using a stale
reference `aste_array_class`.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I191907c0053456bb57de425aa6ccd9668df818a2
diff --git a/runtime/native/java_lang_VMClassLoader.cc b/runtime/native/java_lang_VMClassLoader.cc
index b1511c0..42c7ad5 100644
--- a/runtime/native/java_lang_VMClassLoader.cc
+++ b/runtime/native/java_lang_VMClassLoader.cc
@@ -37,11 +37,11 @@
 // A class so we can be friends with ClassLinker and access internal methods.
 class VMClassLoader {
  public:
-  static mirror::Class* LookupClass(ClassLinker* cl,
-                                    Thread* self,
-                                    const char* descriptor,
-                                    size_t hash,
-                                    ObjPtr<mirror::ClassLoader> class_loader)
+  static ObjPtr<mirror::Class> LookupClass(ClassLinker* cl,
+                                           Thread* self,
+                                           const char* descriptor,
+                                           size_t hash,
+                                           ObjPtr<mirror::ClassLoader> class_loader)
       REQUIRES(!Locks::classlinker_classes_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_) {
     return cl->LookupClass(self, descriptor, hash, class_loader);