Use system.numerics instead of customized struct D2DPoint and D2DMatrix3x2

[jingwood]

Changes

• Use System.Numerics.Vector2 instead of D2DPoint
• Use System.Numerics.Matrix3x2 instead of D2DMatrix3x2
• Make implicit conversion between D2DSize and Vector2

[drewnoakes]

Looks good!

[nikeee]

+1

[drewnoakes]

Given this is a fairly decent API break, are there other API changes we could includes in the next release?

[jingwood]

I am thinking make the Direct 1.1 support available in the next release, if possible...
https://github.com/jingwood/d2dlib/milestone/1

What do you think?

[drewnoakes]

I've commented on #60.

[nikeee]

In the nud2dlib fork, I've done some work to better support C#'s non-nullable-reference-types:
nikeee/nud2dlib@83843e8

I also fiddled around with SuppressGCTransition in this commit:
nikeee/nud2dlib@79361de
I'm not sure if adding the attribute was/is valid in this case (it's a long time ago). But it was ment to improve the performance of pinvoke calls to the native DLL (see linked article).

There were also some unused resources: nikeee/nud2dlib@8ea17c3

Maybe these kinds of simplifications would be something worth to backport:
nikeee/nud2dlib@e5ebacb
nikeee/nud2dlib@5e4030f

If you're in on some of these, I'd be happy to file some PRs.