Collapse ART's AbstractMethod class into Executable

After the OpenJDK 8 pull there is now a common base class
for Method and Constructor that can be used instead.

Methods that are abstract on Executable but on Android
were implemented in AbstractMethod are now consistently
renamed to "{method}Internal", declared final and
given package-protected access.

For consistency with all other private, natively
implemented methods, the method getDeclaredAnnotations()
has been renamed getDeclaredAnnotationsNative().

Bug: 28666126
Bug: 31052885
Test: make test-art-host and cts run of CtsLibcoreTestCases
Change-Id: Ibfe6af6a47fe0cfffd0859ffbe58980aeb84e053
diff --git a/runtime/art_method.cc b/runtime/art_method.cc
index fd6c37a..193bea1 100644
--- a/runtime/art_method.cc
+++ b/runtime/art_method.cc
@@ -34,8 +34,8 @@
 #include "jit/jit_code_cache.h"
 #include "jit/profiling_info.h"
 #include "jni_internal.h"
-#include "mirror/abstract_method.h"
 #include "mirror/class-inl.h"
+#include "mirror/executable.h"
 #include "mirror/object_array-inl.h"
 #include "mirror/object-inl.h"
 #include "mirror/string.h"
@@ -52,9 +52,9 @@
 
 ArtMethod* ArtMethod::FromReflectedMethod(const ScopedObjectAccessAlreadyRunnable& soa,
                                           jobject jlr_method) {
-  auto* abstract_method = soa.Decode<mirror::AbstractMethod*>(jlr_method);
-  DCHECK(abstract_method != nullptr);
-  return abstract_method->GetArtMethod();
+  auto* executable = soa.Decode<mirror::Executable*>(jlr_method);
+  DCHECK(executable != nullptr);
+  return executable->GetArtMethod();
 }
 
 mirror::String* ArtMethod::GetNameAsString(Thread* self) {