Squashed 'Source/OpenTK/Platform/SDL2/sdl2-cs/' content from commit 58a8d31

git-subtree-dir: Source/OpenTK/Platform/SDL2/sdl2-cs
git-subtree-split: 58a8d318ac7ea970fe0f1ecae13eac6151dce7f9
Merge commit 'fd9d306b2a5cbe882f3aa53dab9358e10340e0e5' as 'Source/OpenTK/Platform/SDL2/sdl2-cs'