rbx_xml name mapping for Fire

[LPGhatguy]

For Fire, Size serializes as size_xml, and another property I can't remember has a weird name too. Need to add an XML<->Canonical name mapping for Fire.

[Kampfkarren]

That means this needs to be changed to be class specific instead of broad property names:

https://github.com/LPGhatguy/rbx-dom/blob/9700f1417e2de7f119fc1701138e6a370e84f744/rbx_xml/src/reflection.rs#L13-L19

[LPGhatguy]

I'll probably move it into the rbx_reflection crate eventually, too!

[LPGhatguy]

Foundation for this is in now that #28 is around. I'm currently experimenting with porting rbx_xml over to use rbx_reflection under the hood, which will be known as reflection-guided serialization.