Fix for text width/height ignored/changed to 100 in hardware rendering.

Create a Text object with word wrap on and set a large Text width. This runs fine on Flash, but on CPP targets, the line wraps much sooner. In fact, the call to _field.textWidth returns a curious 100.

I believe this this fails in CPP because Flash.text.TextField uses 100x100 as the default size, and hardware rendering never sets the _field dimensions when a size is passed in. In Flash, updateBuffer sets the _field.width to match the buffer size. The same does not happen for hardware render using the atlas region. This change assigns the _field dimensions in the constructor for hardware rendering.

Possibly it would be better to handle the CPP _field sizing in updateBuffer too, I'm not sure, but this made text sizing work in CPP, at least in my app.