Switch to System.Numerics

[escape-llc]

Summary

Switch to the System.Numerics types for geometry and linear algebra, because they are not defined on device coordinates.

For example, a Rect with negative coordinates configures itself such that negative Y is "higher" than positive Y (device coordinates). This makes representing "world" geometry problematic.

Actual Behavior

Currently using "old style" geometry/linear algebra objects like Rect and Point and Matrix.

Expected Behavior

Easier use of linear algebra in world coordinates.

Additional Details

In particular the Vector2 Vector3 and Matrix3x2 classes can replace existing uses. This also makes it easier to interoperate with Translation which takes a Vector3.