Property accessors

[jasongin]

NAPI is currently missing support for property accessors, to enable C++ callbacks for getters and setters of properties on a wrapped object.

NAN supports this via the Nan::SetAccessor() function, which eventually calls v8::Object::SetAccessor() or v8::ObjectTemplate::SetAccessor(). NAPI currently has functions for getting and setting property values, but not for setting accessors.

From the data I collected, 5 of the top 12 native packages use one or both of those APIs: canvas, fibers, nodegit, sqlite3, zmq. The canvas module implements accessors for several properties like canvas.width, canvas.height, etc. The sqlite3 module only has a single getter for database.open.

[jasongin]

Fixed in the 6.2 branch with 67f4581

To be ported to other branches soon.

[jasongin]

Also done in ChakraCore as 27b3fc7 and merged into the V8 8.x branch as 0bdc1b8