fix: improve file path handling in theme generator script by mmvarma-pro · Pull Request #9426 · RaspberryPiFoundation/blockly

@mmvarma-pro

- Use Path objects from pathlib to handle file paths properly
- Generate output files in the same directory as input file
- Create output filenames with "new_" prefix while preserving original stem name
- Ensure script works with files from any location in the filesystem

@mmvarma-pro

BenHenning