[C++] Cleanup ATNDeserializer interface

[jcking]

This change does a few things. First it changes ATNDeserializer to cache the well known UUIDs using std::call_once which avoids static initialization issues and after the first call has the overhead of only a single atomic load using acquire semantics. Currently the UUIDs are parsed every invocation of the functions.

Secondly it marks a few things as const and removes the virtual specifiers on ATNDeserializationOptions. This is currently not useful as ATNDeserializationOptions is copied in ATNDeserialization so inheriting from the class doesn't accompolish much. Additionally this allows us to inline a bunch of functions giving the compiler a better chance at optimizing things away. Additionally it uses std::call_once to initialize the default options.

Lastly it throws IllegalStateException when marked as read only, instead of throwing a raw C string which is a big no-no.

Note that static initialization order between compilation units is undefined per the C++ standard. To get around this we use std::call_once and std::unique_ptr which both have constant initialization.

[jcking]

@mike-lischke More cleanup/optimization.

[mike-lischke]

Note: most of the methods which are virtual don't need to be that, but the C++ runtime was made to mimic the Java runtime as close as possible. After maturing we can probably now remove some of the virtual specifiers, but we have to be careful, as users might rely on the virtuality in their projects.

[jcking]

Note: most of the methods which are virtual don't need to be that, but the C++ runtime was made to mimic the Java runtime as close as possible. After maturing we can probably now remove some of the virtual specifiers, but we have to be careful, as users might rely on the virtuality in their projects.

In this instance, I think removing virtual is safe. There was no way of overriding the virtual methods and using them with ATNDeserializer as the options are copied by value and not referenced.

[mike-lischke]

@parrt Here's a pure C++ patch, ready for merge.