New SYSLIB diagnostics documents

[jeffhandley]

The following SYSLIB diagnostics from list-of-diagnostics.md (dotnet/runtime) do not have documentation pages created yet. These pages should all be published before .NET 9 GA.

Diagnostic ID	Description	Assignees	PR
SYSLIB1230	Deriving from a GeneratedComInterface-attributed interface defined in another assembly is not supported.	@jkoritzinsky	#42884
SYSLIB5001	Tensor and related APIs in System.Numerics.Tensors are experimental	@tannergooding @michaelgsharp
Experimental	Overview page for experimental APIs	@jeffhandley
SYSLIB5002	SystemColors alternate colors are experimental	@JeremyKuhne
SYSLIB5003	System.Runtime.Intrinsics.Arm.Sve is experimental	@kunalspathak @tannergooding
SYSLIB5004	X86Base.DivRem is experimental since performance is not as optimized as T.DivRem	@kunalspathak @tannergooding
SYSLIB5005	System.Formats.Nrbf is experimental	@adamsitnik

[jeffhandley]

We will also need a new section and Overview added for Experimental APIs, as a peer to [Obsoletions)(https://learn.microsoft.com/dotnet/fundamentals/syslib-diagnostics/obsoletions-overview) and Source-generated code diagnostics.

[JeremyKuhne]

@KlausLoeffelmann this is part of the dark mode experimental feature.