module: make write_bitcode_to_path accept more general path representations

[airwoodix]

Description

Change the function Module::write_bitcode_to_path to accept a AsRef<Path> argument instead of &Path. This allows passing e.g. string slices instead of explicitly building the Path instance, and matches functions in std::fs.

Since &Path is AsRef<Path>, the change is backwards compatible.

How This Has Been Tested

• Adapted the example in the docstring
• The tests checks passing an explicit Path.

Checklist

• [x] I have read the Contributing Guide