fix(source-generators): Methods generated by [GenerateInterfaceMembers] don't match default values for optional arguments with the original method

[DecSmith42]

This pull request enhances the GenerateInterfaceMembersSourceGenerator by improving how interface members are generated and adds a comprehensive test to verify the output. The main changes focus on more accurate handling of method parameters—including ref, in, out, and attributed parameters—when generating class member implementations, ensuring that the generated code matches the interface contract precisely.

Improvements to Source Generation

• Updated the GenerateMethodLine logic to correctly handle all parameter types (including ref, in, out, and attributed parameters), ensuring the generated method signatures and calls accurately reflect the interface definition.
• Changed GeneratePropertyLine and GenerateMethodLine to be private methods for better encapsulation and code clarity.

Testing Enhancements

• Added a new unit test MinimalBuildDefinition_WithGeneratedInterfaceMember_GeneratesSource in GenerateInterfaceMembersGeneratorTests.cs to verify that the generator produces correct source code for a variety of interface member types, including properties, methods with parameters, generics, collections, optional parameters, ref/in/out parameters, and attributed parameters.
• Included a verified output file to demonstrate the expected generated code for the test scenario, covering all supported member types.

[Copilot]

Pull request overview

This pull request fixes a bug in the GenerateInterfaceMembersSourceGenerator where generated method signatures did not properly preserve optional parameter default values, ref/in/out modifiers, and parameter attributes. The fix changes the parameter generation approach from using Roslyn's symbol API to directly extracting parameter syntax via DeclaringSyntaxReferences, ensuring the full parameter declaration (including default values and attributes) is preserved in the generated code.

Key Changes

• Modified GenerateMethodLine to use syntax-based parameter extraction (ToFullString()) instead of symbol-based construction to preserve default values, attributes, and all parameter metadata
• Updated method call parameter generation to correctly handle ref/in/out modifiers
• Added comprehensive test coverage validating the generator works correctly with properties, methods with various parameter types (optional, ref/in/out, attributed), generics, and collections

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

File	Description
DecSm.Atom.SourceGenerators/GenerateInterfaceMembersSourceGenerator.cs	Refactored GenerateMethodLine and GeneratePropertyLine from local functions to private static methods; changed parameter generation from symbol-based to syntax-based approach to preserve all parameter metadata
DecSm.Atom.SourceGenerators.Tests/Tests/GenerateInterfaceMembersGeneratorTests.cs	Added comprehensive test covering interface member generation for properties, methods with various parameter types (optional, ref/in/out, attributed, generic, collections)
DecSm.Atom.SourceGenerators.Tests/Tests/GenerateInterfaceMembersGeneratorTests.MinimalBuildDefinition_WithGeneratedInterfaceMember_GeneratesSource.verified.txt	Verified test output demonstrating correct generation of all tested member types

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