Clean up RelPath API (#38912)

Consolidate constructors and accessors.

Release Notes:

- N/A

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Co-authored-by: Cole Miller <cole@zed.dev>
495a7b0a84Max Brunsfeld committed on 9/25/2025, 9:42:32 PM· committed by GitHubparent301e976
64 files changedLine totals unavailable