Update What's New in .NET 11 for RC 1

[Copilot]

Updates the .NET 11 What's New documentation with RC 1 runtime, library, SDK, and C# changes.

• Overview

  • Summarizes the RC 1 additions across the runtime, libraries, and SDK.

• Runtime

  • Documents expanded Half support and cross-platform in-process crash reporting.

• Libraries

  • Covers process signaling, JSON serialization, cryptography, compression, networking, and numeric APIs.

  • Adds focused examples, including process signaling:

    using Process process = Process.Start("sleep", "30")!;
    process.Signal(PosixSignal.SIGTERM);
    ProcessExitStatus status = process.WaitForExitStatus();

• SDK

  • Documents mobile testing, affected-test selection, reproducible containers, Native AOT reuse, and CLI updates.

• Source mapping

  • Adapts runtime, library, SDK, and C# content from the .NET 11 RC 1 product release notes.
  • Generates overview summaries from the detailed articles.

• Fixes What's new in .NET 11 RC 1 #53528

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Internal previews

File	Preview link
docs/core/whats-new/dotnet-11/libraries.md	Learn preview
docs/core/whats-new/dotnet-11/overview.md	Learn preview
docs/core/whats-new/dotnet-11/runtime.md	Learn preview
docs/core/whats-new/dotnet-11/sdk.md	Learn preview
docs/core/whats-new/dotnet-11/snippets/csharp/Libraries.cs	Learn preview

Build report

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[gewarren]

@copilot Please remove /dotnet/api links if the APIs are new in RC 1 and thus haven't been published to Learn yet. Instead just code fence the API name.

[Copilot]

@copilot Please remove /dotnet/api links if the APIs are new in RC 1 and thus haven't been published to Learn yet. Instead just code fence the API name.

Removed all unpublished RC 1 /dotnet/api links and formatted the API names as inline code in d4d409e.