PackageManager "Staging" call for App Attach fails with ACCESS DENIED if made from inside a container.

### Describe the bug

As originally reported as https://github.com/MicrosoftDocs/winrt-api/issues/2436#issuecomment-5016941773 which was rejected as a product but rather than a documentation bug, you cannot write a modern application that runs inside a MXIS container to manage App Attach packages. We want our management apps to also be written as modern apps, right?

The "staging" option of PackageManager that is required for AppAttach like deployment works just find in an unpackaged traditional application, but the same code fails when inside an MSIX package.

See original report https://github.com/MicrosoftDocs/winrt-api/issues/2436#issuecomment-5016941773

### Steps to reproduce the bug

Write some c# code calling PackageManager to mount, stage, and register an msix package.
Run it outside of a container to show it works.
Put it in a package to show the staging action fails.

### Expected behavior

We expect it to work.

Was on WIndows 11 h5h2 (which is not in the OS pulldown list of this report dialog).

### Screenshots

_No response_

### NuGet package version

latest

### Packaging type

Packaged (MSIX)

### Windows version

Insider Build (xxxxx)

### IDE

_No response_

### Additional context

_No response_

Start with a minimal C# repro using PackageManager to mount, stage, and register an MSIX package. Run the same calls from an unpackaged application and from inside an MSIX container, then investigate why staging returns ACCESS DENIED; done means the packaged scenario behaves as expected or the supported limitation is established.

Written by the indexing model from the issue text.