Fix Resolve-Path -Relative output for dot-prefixed names - #28087

Summary

Fix Resolve-Path -Relative output for dot-prefixed names.

• Distinguish explicit dot-relative segments from path names that begin with a dot
• Prepend the current-directory marker for dot-prefixed relative paths
• Add cross-platform regression coverage

Before the fix

PS:138> dir .abc, delme | Resolve-Path -Relative
.abc\abc.md
.\delme\delme.md
.\delme\loc.ps1
.\delme\locItems.txt

After the fix

PS Q:\yard> dir .abc, delme | Resolve-Path -Relative
.\.abc\abc.md
.\delme\delme.md
.\delme\loc.ps1
.\delme\locItems.txt

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge. If this PR is a work in progress, please open this as a Draft Pull Request and mark it as Ready for Review when it is ready to merge.
• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed