Add MSIXVC2 packaging toggle to "Make a game package"

[elahmed-microsoft]

Adds a checkbox toggle ("Package as MSIXVC2 (.msixvc)") to the package creation view that switches from makepkg.exe to makepkg2.exe pack ... /msixvc2 for creating MSIXVC2 .msixvc packages. The toggle is only visible when makepkg2.exe is installed.

Changes include:

• CheckBox toggle in the package output section, gated on makepkg2 availability
• Process branching: builds makepkg2 pack arguments with /msixvc2 flag when toggled
• Indeterminate progress bar: makepkg2 doesn't emit Encrypted X %, so the progress screen shows a marquee animation and hides the legacy step labels (Validating files / Copying and encrypting / Verifying contents)
• Centered progress layout: remaining elements (image, heading, progress bar) center on screen in MSIXVC2 mode
• Submission Validator parsing: added regex for makepkg2's different log path format (Submission Validator log path: ) so SubVal results display correctly on the finished screen