Modify interop project to prevent winmd leaking from component project

Describe the bug

Referencing a C#/WinRT interop project from a .NET 5 app raises a NETSDK1130 error. This is because the component winmd flows through from the C++/WinRT component project. The project referencing structure is .NET 5 app -> .NET 5 library interop project -> C++/WinRT component.

Look into whether C#/WinRT can fix this either by:

1. Setting the implementation dll as an output in addition to the projection dll for the interop project. Then in the interop project, authors would set <PrivateAssets>all</PrivateAssets> on the project reference to the C++/WinRT component. Caveat is the component might have multiple binaries
2. Modifying cswinrt NuGet targets. Cswinrt needs to influence reference resolution before project references kick in - binlog would show cross-reference target evaluation and the hook for that change. Referring to the CsWinRTRemoveWinMDReferences target here:
   https://github.com/microsoft/CsWinRT/blob/d361800d2cf6a46d2c7d276126a09bab1d8bc1c4/nuget/Microsoft.Windows.CsWinRT.targets#L47

To Reproduce

1. Build the Net5ProjectionSample without generating a NuGet package
2. Add ConsoleAppSample to the sample solution and add a project reference to the interop project, SimpleMathProjection

Here's an example - https://github.com/angelazhangmsft/ProjectionProject

Expected behavior

WinMD doesn't flow through but implementation dll does.

Additional context
Current workaround for consuming interop project by project reference is to add cswinrt NuGet reference in app

Reproduce the issue in src/Samples/Net5ProjectionSample by adding ConsoleAppSample and referencing SimpleMathProjection without generating a NuGet package. Start with the referenced Microsoft.Windows.CsWinRT.targets file, especially the CsWinRTRemoveWinMDReferences target, and inspect the project-reference evaluation shown in a binlog. Done means the WinMD no longer flows through the interop project while its implementation DLL does.