Add a type helper to local data-flow analysis

[meziantou]

Summary

• Add a reusable type helper to LocalDataFlowAnalysis.
• Refactor analyzers to use the shared helper for type checks and data-flow analysis.
• Extend coverage with focused unit tests for the helper and affected analyzers.

Testing

• Added and updated analyzer unit tests covering the new type-analysis behavior and related diagnostics.
• Not run (not requested).