Deserialize annotations from package$src files if needed

For top-level members, we now write a FQ name of the package$src class which
has the member's annotations, and read the correct file in deserialization

compiler/frontend.java/serialization.java/src/java_descriptors.proto

@@ -69,4 +69,7 @@ extend Callable {
   optional JavaMethodSignature method_signature = 100;
 
   optional JavaPropertySignature property_signature = 101;
+
+  // For top-level callables, short name of "...Package$src$..." class with the callable's body and annotations
+  optional int32 src_class_name = 102;
 }