Libraries and runtime updates in .NET 9 Preview 6

[richlander]

Here's what's new in .NET Libraries:

• Improvements to System.Numerics
• Support Primary Constructors in Logging Source Generator
• System.Text.Json
• [GeneratedRegex] on properties
• Regex.EnumerateSplits
• OrderedDictionary<TKey, TValue>
• ReadOnlySet<T>
• allows ref struct used in many places throughout the libraries
• Collection lookups with spans
• More span-based APIs
• Base64Url
• SocketsHttpHandler by default in HttpClientFactory
• TLS resume with client certificates on Linux
• System.Net.ServerSentEvents
• Introducing the Metrics Gauge Instrument

Here's a summary of what's new in the .NET Runtime:

• ARM64 Code Generation
• Code Layout
• Loop Optimizations
• Reduced Address Exposure
• AVX10v1 Support
• Hardware Intrinsic Code Generation
• Constant Folding for Floating Point and SIMD Operations

Release notes:

• Libraries release notes
• Runtime release notes

.NET 9 Preview 6:

• Discussion
• Release notes
• What's new in .NET 9