Fixing WACK failure on store submission

[llongley]

The store expectations for WACK certification are somewhat finicky - they need a WinMD to appear in the WinMetadata folder (and in the root) when that WinMD is implemented by a framework package (which is the case for our stable releases), but they need that WinMD to not appear in the WinMetadata folder when that WinMD is implemented by a DLL in the AppX file (which is the case for our prereleases).

Frustratingly, this restriction appears to only be enforced when actually submitting to the store - the local app cert kit does not report any issues; it's only when you upload the appxupload/msixupload file to the store that it complains. Additionally, there does not appear to be any way to locally run validation on that appxupload/msixupload file, so there's no way for me to add a check to ensure that we won't hit this in the future. I've manually uploaded a test app built with these changes and submitted it to the store, and confirmed that it passed certification there.

There's also a separate item group for items to be added to the appxupload/msixupload file, which also needs to have our WinMD added to it. I've done that, too.

Fixes #3780

[llongley]

/azp run

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