Does not work with shared project

[nvmkpk]

Describe the bug
This code file does not get generated when using a shared project (.shproj) for sharing code between Visual Studio 2019 and 2022 and the .vsct file is in the shared project.

To Reproduce
Steps to reproduce the behavior:

1. Create two menu extension projects, one for VS2019 and another for VS2022.
2. Create a shared project (with extension .shproj)
3. Move all code and .vsct files to the shared project
4. Right click on the .vsct file and click on Synchronize To Code File
5. Notice that the above step does nothing.
6. Manually change the `.projitems' file to what the above menu item does
7. Build the project and notice that the build fails due to missing generated .cs file for the .vsct file.

Expected behavior
The .cs file gets generated and build succeeds

[tonyhallett]

The vsct should be a shared file and not in the shared project.
See 6. https://learn.microsoft.com/en-us/visualstudio/extensibility/migration/update-visual-studio-extension?view=vs-2022
Then the VsixSynchronizer works.