Allow dotnet test --list-tests json for Microsoft.Testing.Platform

[Evangelink]

Fixes #49754

The MTP side added support for --list-tests json in microsoft/testfx#8280. This PR plumbs the optional text/json value through the SDK CLI so users can do:

dotnet test --list-tests json
dotnet test --list-tests text
dotnet test --list-tests        # (unchanged: no value = text behavior)

Changes

• TestCommandDefinition.MicrosoftTestingPlatform.ListTestsOption: arity Zero → ZeroOrOne, restrict accepted values to text/json via AcceptOnlyFromAmong, dedicated HelpName and a new resource string CmdMTPListTestsDescription.
• TestOptions: new ListTestsArgument field.
• MicrosoftTestingPlatformTestCommand: read the option value and pass it through.
• TestApplication.GetArguments: forward the value to the test host (escaped) when present; absent value still emits a bare --list-tests token (no behavioral change for users today).
• Tests:
  • New theory DiscoverTestProjectForwardsListTestsArgument (Debug/Release × text/json) asserts the value is forwarded as a separate arg.
  • New theory DiscoverTestProjectRejectsInvalidListTestsArgument asserts foo/JSON/TEXT are rejected (validator is case-sensitive, matching MTP's lowercase keys).
  • Existing DiscoverTestProjectWithCustomRunArgumentsAndTestEscaping continues to assert the bare --list-tests token forwarding when no value is provided.
• Snapshot MTPHelpSnapshotTests.VerifyMTPHelpOutput.verified.txt updated for the new help line.

Follow-up

The full end-to-end JSON output also requires a fix on the MTP side: TerminalOutputDevice.ConsumeAsync and DisplayAfterSessionEndRunAsync currently early-return when _isServerMode is true (which the SDK always sets via --server dotnettestcli), so today MTP buffers/emits no JSON when invoked through dotnet test. I'll file a follow-up issue in microsoft/testfx to address that.

[Copilot]

Pull request overview

This PR adds SDK CLI plumbing for Microsoft.Testing.Platform’s dotnet test --list-tests optional output format, enabling text or json to be forwarded to the test host.

Changes:

• Updates the MTP --list-tests option to accept text|json and forwards the selected value.
• Adds test coverage for forwarding valid values and rejecting invalid values.
• Updates help text, snapshots, and localization resources for the new option description.

Show a summary per file

File	Description
src/Cli/Microsoft.DotNet.Cli.Definitions/Commands/Test/TestCommandDefinition.MicrosoftTestingPlatform.cs	Changes --list-tests option arity and accepted values.
src/Cli/Microsoft.DotNet.Cli.Definitions/CommandDefinitionStrings.resx	Adds MTP-specific list-tests description.
src/Cli/dotnet/Commands/Test/MTP/MicrosoftTestingPlatformTestCommand.cs	Reads the optional list-tests value from parsing.
src/Cli/dotnet/Commands/Test/MTP/Options.cs	Adds storage for the list-tests argument.
src/Cli/dotnet/Commands/Test/MTP/TestApplication.cs	Forwards the list-tests value to the test application.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndDiscoversTests.cs	Adds valid/invalid list-tests argument tests.
test/dotnet.Tests/CommandTests/Test/snapshots/MTPHelpSnapshotTests.VerifyMTPHelpOutput.verified.txt	Updates expected help output.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.cs.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.de.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.es.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.fr.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.it.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.ja.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.ko.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.pl.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.pt-BR.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.ru.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.tr.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.zh-Hans.xlf	Adds localized resource entry placeholder.
src/Cli/Microsoft.DotNet.Cli.Definitions/xlf/CommandDefinitionStrings.zh-Hant.xlf	Adds localized resource entry placeholder.

Copilot's findings

• Files reviewed: 20/20 changed files
• Comments generated: 1

[Evangelink]

Moving back to draft so I can double check something.

[Evangelink]

Closing in favor of the protocol-based approach. The MTP IPC wire contract already carries the full discovered-test payload the SDK needs (Uid, DisplayName, FilePath, LineNumber, Namespace, TypeName, MethodName, ParameterTypeFullNames, Traits) — vendored from microsoft/testfx and already on \main\ (commit cd590b6). In --list-tests\ mode the SDK already handshakes as \Discover\ and receives \DiscoveredTestMessages\ over the pipe.

Rather than forwarding --list-tests json\ to the test host (which is blocked today because MTP's \TerminalOutputDevice\ early-returns under _isServerMode, always set via --server dotnettestcli), the SDK will render the JSON itself from the messages it already receives. This avoids the testfx server-mode change, avoids stdout interleaving, and matches the preference for the SDK acting as the discovery client. A follow-up PR will implement the SDK-side rendering.