Reimplement certain Builtin types in Dart

[fuzzybinary]

godot-cpp doesn't generate a lot of the builtin types, especially the math heavy ones, as going back and forth through the Godot calling system would be cumbersome. Instead, they re-implement them in C++

We should take a similar approach in Dart, only copying values out to opaque memory when needed. The classes that should get this treatment are:

• aabb
• basis
• color
• plane
• projection
• quaternion
• rect2
• rect2i
• transform2d
• transform3d
• vector2
• vector2i
• vector3
• vector3i
• vector4
• vector4i

This will also allow us to simplify their interfaces, including allowing default parameters for constructors instead of using named constructors for everything but the default.