Project Reference support for WinRT Components

[j0shuams]

Description

Note: this a rebase of the same PR made for .NET 5 -- #19218

Authoring C#/WinRT components has been working towards supporting native and managed consumers. This PR provides the needed changes to support consumers using project references. To do so, we must have some custom logic for Windows Runtime components.

Components typically output a .dll, but C#/WinRT components output a .winmd, which has a general implementation .dll "WinRT.Host.dll". This has complicated getting user scenarios working, as multiple assemblies need to be distributed for "one" assembly.

I am proposing we add a property in an existing target, which was made for WinRT support recently. As well as add a new target that uses the property set in the existing target to add a reference. We need this to support C# project reference consumers. Because C# consumers only get a .winmd via GetTargetPath, they do not have the assembly containing the managed implementation, so we annotate the .winmd to have the path to the implementation, and we add it as a reference here.

(FWIW: C++ consumers use the WinRT.Host.dll as the implementation assembly for the component.)

Customer Impact

Native app (C++) developers should be able to reference WinRT components made with C#/WinRT simply by adding a project reference. This PR removes the need for a project reference and a reference to the winmd made by the project -- the latter of which required an extra build step before the reference could be added.

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Verification

• Manual (required)
• Automated

I have opened an issue to track adding the automated validation - microsoft/CsWinRT#958

[dsplaisted]

It would be good to link the previous PR. Also FYI, you can change the target branch of an existing PR with the "edit" button, though sometimes that picks up commits you don't want so you need to make sure it did the right thing afterwards.