Expand `~` to `$home` on Windows with tab completion

[SteveL-MSFT]

PR Summary

https://github.com/PowerShell/PowerShell/pull/19489 added some improvements to tab-completion, but one side effect is that on Windows, a ~ is retained instead of being expanded. Since ~ is not understood by native commands, this breaks many use cases.

This change only retains ~ on non-Windows systems.

PR Context

Fix https://github.com/PowerShell/PowerShell/issues/20750

PR Checklist

• [x] PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• [x] Summarized changes
• [x] Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• [x] This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: or [ WIP ] to the beginning of the title (the WIP bot will keep its status check at Pending while the prefix is present) and remove the prefix when the PR is ready.
• Breaking changes
  • [x] None
  • OR
  • [ ] Experimental feature(s) needed
    • [ ] Experimental feature name(s):
• User-facing changes
  • [x] Not Applicable
  • OR
  • [ ] Documentation needed
    • [ ] Issue filed:
• Testing - New and feature
  • [ ] N/A or can only be tested interactively
  • OR
  • [x] Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • [x] I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
  • OR
  • [ ] I have considered the user experience from a tooling perspective and opened an issue in the relevant tool repository. This may include:
    • [ ] Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode (which runs in a different PS Host).
      • [ ] Issue filed:
    • [ ] Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
      • [ ] Issue filed:
    • [ ] Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
      • [ ] Issue filed:
    • [ ] Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).
      • [ ] Issue filed:

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Microsoft Forms

[adityapatwardhan]

Wait on a preview release before considering for 7.4