[LifetimeSafety] Reorganize code into modular components (#162474)

Restructure the C++ Lifetime Safety Analysis into modular components
with clear separation of concerns.

This PR reorganizes the C++ Lifetime Safety Analysis code by:

1. Breaking up the monolithic `LifetimeSafety.cpp` (1500+ lines) into
multiple smaller, focused files
2. Creating a dedicated `LifetimeSafety` directory with a clean
component structure
3. Introducing header files for each component with proper documentation
4. Moving existing code into the appropriate component files:
    - `Checker.h/cpp`: Core lifetime checking logic
    - `Dataflow.h`: Generic dataflow analysis framework
    - `Facts.h`: Lifetime-relevant events and fact management
    - `FactsGenerator.h/cpp`: AST traversal for fact generation
- `LiveOrigins.h/cpp`: Backward dataflow analysis for origin liveness
- `LoanPropagation.h/cpp`: Forward dataflow analysis for loan tracking
    - `Loans.h`: Loan and access path definitions
    - `Origins.h`: Origin management
    - `Reporter.h`: Interface for reporting lifetime violations
    - `Utils.h`: Common utilities for the analysis

The code functionality remains the same, but is now better organized
with clearer interfaces between components.

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