Add angle renderer support (aka "compatibility mode")

[peppy]

We don't yet have good backwards compatibility support for older hardware, where the hardware (or drivers) don't support the OpenGL standards we rely on.

This covers adding the same level of compatibility that we have in osu-stable. It should preferably be an automatic fallback whenever opengl fails to initialise.

[huupoke]

I doubt if this is even practical to do anymore, since those hardware probably can't even run Windows 8.1 (no driver support). And .NET 6 only supports Windows 7 ESU, which probably only be purchased in enterprise environments.

[smoogipoo]

We won't be using ANGLE. We'll be using Veldrid and have native D3D/Vulkan support.

[peppy]

Also to keep in mind is that this isn't about "hardware older than Windows 8.1", but hardware/drivers which support D3D better than OpenGL.