MethodHandles: Enable return value conversions.

Enables return values conversions and simplify the type conversion
logic. Ensures check for WrongMethodTypeExceptions before invoking a
method handle.

Test: m test-art-host-run-test-956-methodhandles
Bug: 30550796

Change-Id: I8add3ad0a19b43010946b4fb9f1c0f0949287860
diff --git a/runtime/method_handles.h b/runtime/method_handles.h
index 0cc69f2..54c772a 100644
--- a/runtime/method_handles.h
+++ b/runtime/method_handles.h
@@ -59,6 +59,16 @@
   return handle_kind <= kLastInvokeKind;
 }
 
+// Returns true if there is a possible conversion from |from| to |to|
+// for a MethodHandle parameter.
+bool IsParameterTypeConvertible(ObjPtr<mirror::Class> from,
+                                ObjPtr<mirror::Class> to);
+
+// Returns true if there is a possible conversion from |from| to |to|
+// for the return type of a MethodHandle.
+bool IsReturnTypeConvertible(ObjPtr<mirror::Class> from,
+                             ObjPtr<mirror::Class> to);
+
 // Performs a conversion from type |from| to a distinct type |to| as
 // part of conversion of |caller_type| to |callee_type|. The value to
 // be converted is in |value|. Returns true on success and updates