Stencil isn't working on Veldrid renderers

[EVAST9919]

OpenGL/LegacyGL	D3D

[frenzibyte]

This is also the case on Metal, it shows white circles instead. To start off:

osu-framework/osu.Framework/Graphics/Veldrid/VeldridRenderer.cs

Line 98 in 9df4c9e

SwapchainDepthFormat = PixelFormat.R16_UNorm,

This line doesn't specify a stencil attachment, it should be changed to D24_UNorm_S8_UInt or D32_Float_S8_UInt (note the former isn't supported on all Metal GPUs).