Add support for .appxupload files as InstallerUrl-s in manifests.

Relevant area(s)

WinGet CLI

Description of the new feature / enhancement

Although it can be counted on two hands (possibly one) how many app devs that make their .appxupload files publicly available as standalone files, adding support for it would come with the remarkable benefit that it'd make Winget able to install them whereas App Installer doesn't.

Cases I know of at the time of writing (1 listed case per publisher):

• https://get.videolan.org/vlc-winrt/3.1.0/VLC_WinRT.Windows_3.1.0.0_Test/VLC_WinRT.Windows_3.1.0.0_x86_arm_bundle.appxupload.zip
• https://cdn.kde.org/ci-builds/network/kdeconnect-kde/release-25.08/windows/kdeconnect-kde-release_25.08-5537-windows-cl-msvc2022-x86_64.appxupload
• https://resources.oreilly.com/examples/9781849686709/-/raw/master/6709EN_Code/6709EN_Code/6709_06_codes/ApplicationLifecycleSample/ApplicationLifecycleSample/AppPackages/ApplicationLifecycleSample_1.0.0.1_AnyCPU_Debug.appxupload

Proposed technical implementation details

Allow the use of .msu files in InstallerUrl-s, in much the same way as what is the case at the time of writing with .msix/.appx/.msixbundle/.appxbundle.

Start in the WinGet CLI code that handles InstallerUrl values for .msix, .appx, .msixbundle, and .appxbundle files. Trace how those URLs are validated and installed, and clarify the issue's conflicting references to .appxupload and .msu. Done means the intended .appxupload cases are accepted and installed through InstallerUrl handling, with corresponding tests where that behavior is covered.