Bug in xcproject - new pages for playgrounds

[miguelangel-dev]

Description

Sometimes, if you copy-paste, an existing playground in an existing nef project, the logic tree for Xcode project gets absolute paths instead of relative.

While Apple fixes it in Playgrounds - we should take it in mind for generators (jekyll, markdown, carbon...)

Example

if I have a nef project BugTesting, and I link an external playground (ex. Playground.playground) - this should be linked like relative path ./Playground.playground - but if we explore logic tree we will read /User/<username>/BugTesting/Playground.playground (it is a wrong Apple behaviour)