Use sensible defaults for depth/stencil

[Perksey]

Closes #1863

[ThomasMiz]

Should we update the SDL backend too? The current relevant code looks like this:

            Sdl.GLSetAttribute(GLattr.DepthSize,
                    opts.PreferredDepthBufferBits is null || opts.PreferredDepthBufferBits == -1
                        ? 24 : opts.PreferredDepthBufferBits.Value);

            Sdl.GLSetAttribute(GLattr.StencilSize,
                    opts.PreferredStencilBufferBits is null || opts.PreferredStencilBufferBits == -1
                        ? 8 : opts.PreferredStencilBufferBits.Value);

So the only difference is that if one of these options is set to null, it uses 24/8 instead of the system default.

Everything looks good though

[Perksey]

Yeah I agree, but I’m not sure that SDL has “system default” functionality. This PR was mostly to align it with SDL for the common case. I’ll double check to make sure.

[Perksey]

Couldn’t find anything equivalent to GLFW’s don’t care… maybe not setting the attributes does that. I’ll give that a go.

[Perksey]

@ThomasMiz Slightly adjusted the SDL logic, PTAL