Add support for formatting file-based apps

[jjonescz]

Resolves #49285.

(Note that this is currently stacked on top of #55595 because it needs roslyn version from that flow. The CI failures are also unrelated to this PR as they appear in that parent PR too.)

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[Copilot]

Pull request overview

This PR updates dotnet format to accept C# file-based programs (e.g., dotnet format app.cs) by treating eligible .cs entrypoint files as valid “workspace” inputs, updating workspace loading behavior to correctly scope formatting, and adding regression tests and localized help text.

Changes:

• Extend workspace discovery/help text to allow project/solution or file-based program inputs.
• Track the loaded ProjectId when opening a single project workspace so referenced projects are excluded reliably.
• Add unit + CLI scenario tests (and test assets) covering formatted/unformatted file-based apps.

Reviewed changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/TestAssets/dotnet-format/for_code_formatter/file_based_app/unformatted.cs	New unformatted file-based app input for formatter tests.
test/TestAssets/dotnet-format/for_code_formatter/file_based_app/formatted.cs	New formatted baseline for file-based app formatter tests.
test/dotnet.Tests/CommandTests/Run/RunFileTests_BuildCommands.cs	Adds CLI-level regression test for dotnet format app.cs.
test/dotnet-format.UnitTests/MSBuild/MSBuildWorkspaceLoaderTests.cs	Updates tests for new LoadedWorkspace return type.
test/dotnet-format.UnitTests/CodeFormatterTests.cs	Adds file-based app formatting coverage and treats .cs as project workspace in test helper.
test/dotnet-format.UnitTests/Analyzers/ThirdPartyAnalyzerFormatterTests.cs	Updates for new LoadedWorkspace API.
src/Dotnet.Format/dotnet-format/xlf/Resources.zh-Hant.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.zh-Hans.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.tr.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.ru.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.pt-BR.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.pl.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.ko.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.ja.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.it.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.fr.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.es.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.de.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/xlf/Resources.cs.xlf	Localization updates for new/renamed workspace argument strings.
src/Dotnet.Format/dotnet-format/Workspaces/MSBuildWorkspaceLoader.cs	Changes loader to return LoadedWorkspace including ProjectId.
src/Dotnet.Format/dotnet-format/Workspaces/MSBuildWorkspaceFinder.cs	Accepts file-based program entrypoints as workspace inputs; updates invalid-workspace error.
src/Dotnet.Format/dotnet-format/Resources.resx	Updates help/error strings to include file-based apps.
src/Dotnet.Format/dotnet-format/dotnet-format.csproj	Adds project reference needed for file-based program support.
src/Dotnet.Format/dotnet-format/Commands/FormatCommandCommon.cs	Updates argument name/description to reflect new accepted inputs.
src/Dotnet.Format/dotnet-format/CodeFormatter.cs	Uses ProjectId-based scoping when formatting a single project workspace.

[jjonescz]

/azp run

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