Add clr tests

[ktmitton]

This is my first attempt to write some tests before making some more complex changes. I stubbed out CitizenFX.Core.Native.API with a spy I could use to monitor the side-effects.

I also stubbed out some stuff in CitizenFX.Core, the bare minimum to get BaseTests.InitializeOnAdd() to run, but long-term I can see those stubs being replaced with their real implementations. That would involve mocking out more of API, though, which is why I avoided it for this first pass.

[ktmitton]

@blattersturm I realize I may have tagged the wrong person before, but I'm not sure what the process is here. What's the best way to go about getting this PR reviewed/approved? I'm holding off on making additional changes until I know this is a good path to take, avoid putting in a bunch of time for something that may not be accepted.

[blattersturm]

I'm not sure myself either - perhaps best to discuss changes you want to actually make beforehand as otherwise it ends up with stuff like this that otherwise looks very out of place and doesn't help anyone.

These tests could be useful to someone else but again I don't think they fit in the repo at this time (and especially not in that path, heh). I'll convert the PR to a draft at least so in case someone else seems them as useful they're there.

[thorium-cfx]

Uh finger slipped :/ phone... that button was huge

Edit: I didn't see this as any benefit to my testing, but yes maybe others see more use in it.