Document ArtifactsProjectName property in artifacts output layout

[Copilot]

The artifacts output layout docs don't mention ArtifactsProjectName, which controls the project name subfolder under artifacts/<output-type>/. The property defaults to $(MSBuildProjectName) and is defined in Microsoft.NET.DefaultOutputPaths.targets.

• Updated the folder structure table to note ArtifactsProjectName as customizable (matching existing pattern for ArtifactsPivots)
• Added configuration example in "How to configure" section:

<PropertyGroup>
  <ArtifactsProjectName>CustomProjectName</ArtifactsProjectName>
</PropertyGroup>

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Internal previews

📄 File	🔗 Preview link
docs/core/sdk/artifacts-output.md	docs/core/sdk/artifacts-output

[Copilot]

Pull request overview

Updates the artifacts output layout documentation to include the ArtifactsProjectName MSBuild property, which controls the project-name subfolder under artifacts/<output-type>/.

Changes:

• Expanded the folder structure table to describe and link customization of the project-name level via ArtifactsProjectName.
• Added a “How to configure” example showing how to set ArtifactsProjectName in a project file.