Use the correct directory separator based on the platform we are working with

[daxian-dbw]

PR Summary

Fix #3923

When working with a remote Runspace, we choose the directory separator based on the platform of the remote server.

Before the fix, the trailing directory separator is \ in a remote session from Windows to Linux

**After the fix, the trailing directory separator is / in a remote session from Windows to Linux

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure you've added one or more new tests tested manually
• Make sure you've tested these changes in terminals that PowerShell is commonly used in (i.e. conhost.exe, Windows Terminal, Visual Studio Code Integrated Terminal, etc.)
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed at PowerShell-Docs
    • Doc Issue filed:

Microsoft Reviewers: Open in CodeFlow

[andyleejordan]

Looks great to me!