Support dotnet pack file.cs

[jjonescz]

Resolves #49369.

[Copilot]

Pull Request Overview

This PR implements support for dotnet pack file.cs to enable packing file-based programs directly from C# source files. The change allows users to create NuGet packages from standalone C# files without requiring a traditional project file structure.

Key changes:

• Modified the PackCommand to detect and handle file-based programs using the virtual project building infrastructure
• Updated command completion descriptions to include C# files as valid inputs
• Added test coverage for the new functionality

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Cli/dotnet/Commands/Pack/PackCommand.cs	Refactored to use CommandFactory pattern and support file-based programs through VirtualProjectBuildingCommand
src/Cli/dotnet/Commands/Pack/PackCommandParser.cs	Updated argument name and description to include C# files as valid inputs
src/Cli/dotnet/Commands/Run/VirtualProjectBuildingCommand.cs	Added PackageOutputPath property and updated runtime config logic to exclude Pack target
test/dotnet.Tests/CommandTests/Run/RunFileTests.cs	Added comprehensive test for pack functionality and updated virtual project templates
test/dotnet.Tests/CommandTests/MSBuild/GivenDotnetPackInvocation.cs	Fixed cast to handle new return type from PackCommand.FromArgs
documentation/general/dotnet-run-file.md	Updated documentation to reflect pack support and clarify behavior
test/dotnet.Tests/CompletionTests/snapshots/zsh/DotnetCliSnapshotTests.VerifyCompletions.verified.zsh	Updated completion description to include C# files

Comments suppressed due to low confidence (1)

[RikkiGibson]

Removing my assignment since I speculate Fred and Chris's sign off will be enough. Let me know if I misunderstood something. Thanks

[jjonescz]

@333fred for another look, thanks

[jjonescz]

Setting both PublishAot=true and PackAsTool=true by default does not currently seem to be possible - #50435.

Hence I've reverted the last commit and I plan to merge this without the PackAsTool=true default for now.