[ios][precompile] refactor header files generator

Replace the regex-based approach for parsing podspec files with a declarative configuration system for header file collection:

Add headers-config.js with explicit podspec configurations defining header patterns, directories, and subspecs

- Add vfs.js to generate VFS overlay YAML files for Clang virtual file system support
- Refactor headers.js to use the new configuration-based approach with support for nested subspecs and path preservation
- Update xcframework.js to handle the new header mapping structure with source/target paths
- This provides more reliable and maintainable header file collection for XCFramework builds by avoiding fragile regex parsing of Ruby podspec files.

Author: chrfalch