Support MSIXVC2 package upload via legacy "Upload a package" path

[elahmed-microsoft]

Adds MSIXVC2 .msixvc package support to the legacy "Upload a package" flow. Previously, selecting an MSIXVC2 package crashed with a GUID parsing error. Now the UI detects, previews, and uploads MSIXVC2 packages by silently rerouting to the makepkg2 upload tool.

Changes include:

• MSIXVC2 detection: Identifies MSIXVC2 packages using ZIP file header signatures
• Info message: Displays an informational message when an MSIXVC2 package is selected, informing the user that upload will use makepkg2
• MSIXVC2-style preview: Extracts metadata from the ZIP's MicrosoftGame.config (StoreId, Identity.Name, DeviceFamily) and shows MSIXVC2-style labels (Destination, Package Identity name, Folder size) while preserving MSIXVC1 preview for legacy packages
• Placeholder image: Adds a placeholder preview image for MSIXVC2 packages since product images cannot be extracted from the packed ZIP
• Upload reroute: On clicking Upload for an MSIXVC2 package, builds makepkg2 upload /pd arguments and navigates to the existing Msixvc2UploadingView progress screen
• makepkg2 availability check: If makepkg2 tools are not installed, the Upload button is disabled with an error message directing the user to install the April 2026 GDK

MSIXVC1 .msixvc and .xvc packages are unaffected... the legacy flow is unchanged