fix: improve file path handling in theme generator script

[mmvarma-pro]

The basics

• I have read https://developers.google.com/blockly/guides/contribute/core#making_and_verifying_a_change

The details

Resolves

Improve file path handling in theme generator script

Proposed Changes

This PR enhances the create_blockStyles.py script to handle input files from any location by:

1. Using Path objects from the pathlib module to properly handle file paths
2. Generating output files in the same directory as the input file
3. Creating output filenames with a "new_" prefix while preserving the original stem name

Reason for Changes

Previously, the script would only work correctly when run from the same directory as the input file. This change makes the script more robust by:

• Ensuring output files are always created in the same directory as the input file
• Using pathlib for cross-platform path handling
• Maintaining a consistent naming convention for output files

This improves developer experience when using the theme generator from different working directories.

Test Coverage

The changes were tested manually by:

• Running the script with input files in the same directory
• Running the script with input files in different directories
• Verifying that output files are created in the expected locations
• Confirming that file content is correctly written

Documentation

No documentation updates are needed as this is an internal improvement to the script's functionality.

Additional Information

This change maintains backward compatibility with existing usage patterns while adding more flexibility for different file locations.

[BenHenning]

Thanks @mmvarma-pro! I don't have a lot of familiarity with the workings of the script, but I also suspect few people on the team do since it hasn't been changed in a long time. The change here makes sense to me and seems like a really solid improvement. I'm happy to accept this change.