Add code fixers for MA0118, MA0161, and MA0186

[meziantou]

Why

These three analyzers already reported useful diagnostics but lacked automatic remediation, which made adoption slower and more manual. This change adds code fixers so developers can apply safe, consistent fixes directly from the IDE.

What changed

• Added a new code fixer for MA0118 ([JSInvokable] methods must be public) that updates method accessibility to public while preserving other modifiers (for example static).
• Added a new code fixer for MA0161 (UseShellExecute must be explicitly set) that offers both actions:
  • Set UseShellExecute to false
  • Set UseShellExecute to true
    and handles both new ProcessStartInfo() and object initializers with existing members.
• Added a new code fixer for MA0186 (Equals/TryGetValue nullable attributes) that:
  • adds or updates [NotNullWhen(true)] on Equals parameters
  • adds or updates [MaybeNullWhen(false)] on TryGetValue out value parameters
• Extended rule tests to validate the new fixers and fix-all behavior patterns for these rules.
• Regenerated documentation with src/DocumentationGenerator, which updated rule source links and the README/docs fixer support matrix.

Notes for reviewers

• MA0161 intentionally exposes two code actions (true/false) because both are semantically valid depending on caller intent.
• The MA0118 tests were split into targeted code-fix cases to align with the test harness behavior that applies one fix option at a time.
• A Roslyn 4.2 targeted run could not be used due to unrelated baseline repository incompatibilities with older APIs; targeted validation was completed on default and Roslyn 4.14.

Validation

• dotnet test tests\Meziantou.Analyzer.Test\Meziantou.Analyzer.Test.csproj --filter "FullyQualifiedName~ProcessStartAnalyzerTests|FullyQualifiedName~MissingNotNullWhenAttributeOnEqualsAnalyzerTests|FullyQualifiedName~JSInvokableMethodsMustBePublicAnalyzerTests" --nologo
• dotnet test tests\Meziantou.Analyzer.Test\Meziantou.Analyzer.Test.csproj /p:RoslynVersion=roslyn4.14 --filter "FullyQualifiedName~ProcessStartAnalyzerTests|FullyQualifiedName~MissingNotNullWhenAttributeOnEqualsAnalyzerTests|FullyQualifiedName~JSInvokableMethodsMustBePublicAnalyzerTests" --nologo
• dotnet run --project src\DocumentationGenerator