feat: add WinGet upgrade option to PowerShell update notification (#5477)

Detects WinGet via 'winget show --id Microsoft.PowerShell', falling back to the winget-pkgs listing when the CLI is missing. The prompt can upgrade with WinGet, install WinGet, and follow WinGet's progress, noting the version WinGet currently has. It is built by a pure buildUpdatePrompt() function, and WinGet options are only offered on Windows.

Author: PtJade-Ceramic