Source Code Transformation for .NET 8

[feO2x]

Closes #135

Source Code Transformation can now target .NET 8

[Copilot]

Pull request overview

This PR updates Light.GuardClauses.SourceCodeTransformation so the single-file export can be flattened for a concrete target framework (netstandard2.0 by default, optionally net8.0), and reworks build validation to compile the generated file against the matching framework using a new Light.GuardClauses.SourceValidation project.

Changes:

• Introduces SourceTargetFramework + SourceFileMergeOptions.TargetFramework, and centralizes Roslyn parse-options creation so both reachability analysis and merging agree on active preprocessor branches.
• Always strips conditional-compilation trivia from the flattened output, and derives polyfill emission from the selected target framework (suppressed for net8).
• Replaces the old Light.GuardClauses.Source compile harness with a multi-targeted Light.GuardClauses.SourceValidation project and updates the build validator + tests accordingly.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Light.GuardClauses.SingleFile.cs	Removes #if/#endif blocks so the committed single-file is explicitly a netstandard2.0-shaped export.
Code/Light.GuardClauses.SourceValidation/Light.GuardClauses.SourceValidation.csproj	Adds a new multi-targeted validation project that compiles an injected generated source file.
Code/Light.GuardClauses.SourceCodeTransformation/SourceTargetFramework.cs	Adds an enum to select netstandard2.0 vs net8.0 export shape.
Code/Light.GuardClauses.SourceCodeTransformation/SourceReachabilityAnalyzer.cs	Adds parse-options factory and threads parse options into catalog parsing for consistent branch selection.
Code/Light.GuardClauses.SourceCodeTransformation/SourceFileMerger.cs	Uses target-framework parse options for the merged output, always removes directives, and derives polyfill emission from target framework.
Code/Light.GuardClauses.SourceCodeTransformation/SourceFileMergeOptions.cs	Adds TargetFramework option and updates default target/output path heuristics.
Code/Light.GuardClauses.SourceCodeTransformation/settings.json	Persists TargetFramework setting (defaults to NetStandard2_0).
Code/Light.GuardClauses.SourceCodeTransformation/Program.cs	Passes TargetFramework into build validation and adjusts default-path application.
Code/Light.GuardClauses.SourceCodeTransformation/GeneratedFileBuildValidator.cs	Builds the new validation project with the selected TFM and injects the generated file path via MSBuild property.
Code/Light.GuardClauses.SourceCodeTransformation.Tests/TestEnvironment.cs	Adds shared test helpers for locating repo directories + temp directories.
Code/Light.GuardClauses.SourceCodeTransformation.Tests/SourceFileMergerWhitelistTests.cs	Updates tests to use shared environment helper and sets explicit target framework in options.
Code/Light.GuardClauses.SourceCodeTransformation.Tests/SourceFileMergerFrameworkTests.cs	Adds tests for net8 vs netstandard export surface, directive removal, polyfill behavior, and validation.
Code/Light.GuardClauses.SourceCodeTransformation.Tests/ParseCSharpFilesWithRoslynTests.cs	Uses shared environment helper instead of duplicated directory discovery.
Code/Light.GuardClauses.SourceCodeTransformation.Tests/GeneratedFileBuildValidatorTests.cs	Updates build validation tests to the new validation-project approach.
Code/Light.GuardClauses.Source/Light.GuardClauses.Source.csproj	Removes the old netstandard-only compile-check harness project.
Code/Light.GuardClauses.AllProjects.sln	Swaps Light.GuardClauses.Source for Light.GuardClauses.SourceValidation in the solution.
Code/ai-plans/0135-source-code-transformation-for-dotnet-8.md	Adds an implementation plan/traceability document for issue #135.

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