FilteringPathname bug fixes and improvements

Document filter consistency requirement.

Implement glob method.

Make + always return a filtered pathname.

Ensure that to_s always returns the input pathname as a string.

Improve handling of relative pathname results.

Ensure only absolute pathnames are passed to the filter.

Clean pathnames before filtering.

[#61738342]
Merge 61738342-FilteringPathname-improvements to master

[Completes #61738342]