Consolidate file-level directive separators

[jjonescz]

Resolves #48841.

[Copilot]

Pull Request Overview

This PR consolidates and unifies the separators used in file-level directives across the codebase, tests, and documentation. The key changes include updating tests to use “@” for sdk/package directives and “=” for property directives, revising error messages in multiple localization files, and refactoring parsing logic in the VirtualProjectBuildingCommand.

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/Run/RunFileTests.cs	Updated separator for package directives in test cases
test/dotnet.Tests/CommandTests/Project/Convert/DotnetProjectConvertTests.cs	Revised test expectations for sdk, package, and property directives
src/Cli/dotnet/Commands/xlf/*	Updated error message text and notes for invalid directive names and missing parts
src/Cli/dotnet/Commands/Run/VirtualProjectBuildingCommand.cs	Refactored ParseOptionalTwoParts to use an explicit separator and added a regex check for disallowed characters
src/Cli/dotnet/Commands/CliCommandStrings.resx	Updated resource strings to match the new directive separator requirements
documentation/general/dotnet-run-file.md	Adjusted documentation to reflect the updated usage of separators

Comments suppressed due to low confidence (1)

src/Cli/dotnet/Commands/Run/VirtualProjectBuildingCommand.cs:913

• The updated signature that requires an explicit separator improves clarity. It would be helpful to document this change in the method summary, explicitly noting that 'package' directives use '@' and 'property' directives use '='.

private static (string, string?)? ParseOptionalTwoParts(..., char separator)

[RikkiGibson]

micro-nit to make it clear that directiveText is always converted to span. Take it or not at your discretion.

Suggested change

	var firstPart = (i < 0 ? directiveText : directiveText.AsSpan(..i)).TrimEnd();
	var firstPart = directiveText.AsSpan(..(i < 0 ? ^0 : i)).TrimEnd();

[RikkiGibson]

This shows that if user prefers to do #:property Prop = Value, they can do that with an equivalent result to #:property Prop=Value, right?

[jjonescz]

Right, there is also test Directives_Whitespace which probably shows this more directly.

[jjonescz]

@MiYanni for a review, thanks