feat: Add Navigation Support for FindPackageShare and get_package_share_directory

[tibisabau]

Description

This PR implements navigation support for FindPackageShare and get_package_share_directory functions in the LaunchMap parser. The parser now resolves these calls to actual filesystem paths using ROS 2's ament_index_python.packages.get_package_share_directory, while maintaining backward compatibility with the existing symbolic expression format.

Implementation Details

• Created package_path_resolver.py utility module to handle package path resolution with graceful error handling
• Enhanced FindPackageShare handler to include resolved_path field in output when package is available
• Modified get_package_share_directory resolver to return structured dict with both symbolic expression and resolved path
• Updated postprocessing logic to properly distinguish between launch constructs (no quotes in PathJoinSubstitution) and Python function calls (with quotes)
• Added comprehensive unit tests to verify both resolution functionality and error handling

The implementation gracefully handles cases where:

• ament_index_python is not available (warns but continues)
• Package cannot be found (warns but continues)
• Package is found (includes resolved_path in output)

Closes #52.

Checklist if Applicable

• The tests passed – npm run test:parser (94 passed, 1 skipped)
• Linting passed – npm run lint:py (All checks passed!)
• Documentation has been added
• CHANGELOG.md has been updated