Support PowerShell profile modification on Windows for both Windows PowerShell and pwsh

[dsplaisted]

Summary

Follow-up from the shell profile work in #53447.

dotnetup currently uses a single PowerShell shell provider and only wires profile modification for the Unix pwsh location. We still need a Windows-specific implementation that correctly handles both Windows PowerShell and PowerShell 7+.

Proposed work

• detect and update the correct PowerShell profile location(s) on Windows
• investigate $PROFILE usage and the host-specific profile search order
• handle Documents / OneDrive redirection and other non-default home-directory layouts
• decide whether dotnetup should modify only the active PowerShell flavor or both by default
• keep the generated script compatible across both shells where possible
• add regression tests for the Windows profile path logic

Related

• Dotnetup: Shell profile modification for PATH and DOTNET_ROOT #53447
• dotnetup: Improve shell detection #52939

[dsplaisted]

Related review comments:

• Dotnetup: Shell profile modification for PATH and DOTNET_ROOT #53447 (comment)
• Dotnetup: Shell profile modification for PATH and DOTNET_ROOT #53447 (comment)

[nagilson]

Suggestion from the comment (as copilot with the git mcp server is having trouble loading the PR comment, there are too many comments)

1. What if we rename the class in this PR to be PwshCoreEnvShellProvider and we can inherit it from the WindowsPowershellEnvShellProvider in the next PR? I'd also add a comment to the paths returned mentioning it's linux based for now.
2. Where does .config come from ? I believe, and on my machine at least:
   $HOME\OneDrive - Microsoft\Documents\PowerShell (pwsh)
   $HOME\OneDrive - Microsoft\Documents\WindowsPowerShell (pwsh)

However, I don't see a consistent want to know if there's some weird injection like one drive over the documents folder layer. $HOME\Documents is actually empty for me.

$HOME/.config/powershell/ is correct but only on unix, so this is somewhat confusing to me.

I would also say - $PROFILE can be modified and we should probably search that first and then see if exists on disk and is a .ps1 file, then prefer that.

[nagilson]

completed by #54520