Fix recognizing dotnet ./file.cs with special arguments

[jjonescz]

Fixes #49892.

If dotnet ./Program.cs build is encountered, the command line is parsed as the BuildCommand, not RootCommand, hence I'm removing the check (which I don't think is necessary).

[Copilot]

Pull Request Overview

This PR fixes an issue where dotnet ./file.cs with special arguments wasn't being recognized correctly. The problem occurred when additional arguments were passed (like dotnet ./Program.cs build) because the command line was incorrectly parsed as BuildCommand instead of RootCommand.

• Removes the RootCommand check condition to allow C# file execution regardless of which command parser was used
• Adds comprehensive test coverage for different file path formats and argument combinations

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Cli/dotnet/Program.cs	Removes the RootCommand condition check to fix argument parsing issue
test/dotnet.Tests/CommandTests/Run/RunFileTests.cs	Adds test cases for various file path formats and argument combinations

Comments suppressed due to low confidence (1)

test/dotnet.Tests/CommandTests/Run/RunFileTests.cs:162

• [nitpick] This test case using Path.DirectorySeparatorChar may be redundant with the previous test on line 156 that uses "./Program.cs", since on Unix systems DirectorySeparatorChar is '/' making them identical. Consider testing a backslash scenario specifically or documenting the intent.

        new DotnetCommand(Log, $".{Path.DirectorySeparatorChar}Program.cs")