Very basic D2D compute shader support (non-source generator)

[rickbrew]

Related to #351 and #552, I think there's an opportunity for very basic D2D compute shader support. The first two I was able to do myself with forked code, but the 3rd I would need ComputeSharp to specifically support:

1. Add ComputeShader50 to D2D1ShaderProfile, which would resolve to cs_5_0 / lib_5_0
2. Enable D2D1ShaderCompiler to compile these (might be automatic with # 1)
3. Add [D2DComputeShaderSource] similar to [D2DPixelShaderSource]. I believe this should be trivial?

3 would really help me right now, as I'm currently having to compile my compute shaders at runtime. This causes a noticeable delay the first time one of them is used, and I can't verify it'll even compile until runtime!

I don't think it's necessary to worry about the d2d1computeshaderhelpers.hlsli just yet, that's not what I intend this issue to cover. I just want the basic stuff.

It may also be worth extending this to vertex shaders -- as in, no source generator support but at least we could compile and experiment with them. I don't have any plans to pursue vertex shaders, other than experimenting for satisfying my own curiosity, so this would just be about fleshing out ComputeSharp.D2D1.

[rickbrew]

Also, I have some compute shaders you can copy-paste if you want something for unit testing.