Investigate enhancing interface `PathLike` to support computing relative paths

[ckunki]

Another repo (see IntRef) had the need to compute a relative path for an instance of PathLike.

BFSPY's internal class BucketPath has property path of type PurePath, which offering a method relative_to() but unfortunately path is missing in public interface PathLike.

The current ticket requests investigating to enhance interface PathLike.

Potential approaches

• Add a method relative_to(PathLike other)
• Add property path