Update file-based app functionality in command reference

[meaghanlewis]

Summary

This pull request updates documentation for several .NET CLI commands to support file-based C# apps, and aligns the minimum supported SDK version to .NET 6 across the board. The changes clarify usage and arguments for dotnet build, dotnet clean, dotnet publish, dotnet restore, and dotnet run, and provide new examples for file-based workflows.

Support for file-based C# programs:

• Added support and documentation for using single C# files (<FILE>) as arguments to dotnet build, dotnet clean, dotnet publish, and dotnet restore. This includes updates to synopsis, argument descriptions, and new usage examples. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

• For dotnet run, introduced the --file option and updated documentation to describe running file-based apps, including new argument and usage examples. [1] [2] [3] [4]

Minimum supported SDK version updates:

• Changed the minimum supported SDK version from ".NET Core 3.1 SDK and later" to ".NET 6 and later" in all affected command documentation. [1] [2] [3] [4] [5]

General documentation improvements:

• Updated argument descriptions and usage examples to clarify the behavior when no file is specified, and to better explain the differences between project, solution, and file-based workflows. [1] [2] [3] [4]

• Refreshed dates in front-matter metadata to reflect the latest documentation update. [1] [2] [3] [4] [5]

Fixes #47465

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Internal previews

📄 File	🔗 Preview link
docs/core/tools/dotnet-build.md	dotnet build
docs/core/tools/dotnet-clean.md	dotnet clean command
docs/core/tools/dotnet-publish.md	dotnet publish
docs/core/tools/dotnet-restore.md	docs/core/tools/dotnet-restore
docs/core/tools/dotnet-run.md	dotnet run

[BillWagner]

This looks great to me @meaghanlewis

I had a few comments, most are optional.

[adegeo]

This looks awesome! I found a few things for you to consider. Approving to unblock.