Read-AppxMetadata cmdlet should use IAppxManifestReader.

[jlaanstra]

Currently the Read-AppxMetadata cmdlet extract the package, any packages inside the package until it gets to the AppManifest.xml. This can take more than 5 minutes for large packages.

We should consider using IAppxManifestReader to save 5 minutes or more per build for large packages.

[HowardWolosky]

There are a number of potential drawbacks to adopting IAppxManifestReader (especially given that the API currently only appears accessible via C++).

Distilling the feedback down to its root, the issue appears to be that we're extracting every single file from every single package, as opposed to just extracting the AppxManifest files (since those are all that we actually need).

So, I'd propose that we keep our existing AppxManifest property extraction logic as-is (thus, not adopting IAppxManifestReader, and instead focus on improving our file extraction logic to only extract the manifest files. That should result in a similar packaging time improvement, without the added cost of a new custom module.