Fix NativeAOT WinGet and startup COM paths

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• enumerate WinGet COM-projected collections by index instead of using unsupported IReadOnlyList<T> enumeration
• use raw CoCreateInstance plus the CsWinRT projection for standard WinGet activation
• bypass legacy COM GPU detection and shortcut stamping under NativeAOT, preserving their safe fallbacks

Fixes #5083
Fixes #5085

NativeAOT audit

• The legacy file-picker project is not referenced by the Avalonia publish graph, so it is not a shipped NativeAOT risk.
• Start Menu shortcut AUMID stamping is safely skipped until it can be migrated from legacy COM.
• The DataGrid smooth-scroll reflection hook can be trimmed, falling back to standard scrolling.
• Avalonia DataGrid AOT warnings cover unused automatic-column generation; all app grids use explicit columns and compiled bindings.

Testing

• dotnet test UniGetUI.Windows.slnx --verbosity q --nologo /p:Platform=x64
• Windows x64 NativeAOT publish (Win-x64-NativeAot)