Ability to select Contour as default terminal in Windows 11

[christianparpart]

• get Windows 11 on my Workstation PC :-D
• [DefApp] Document how it works microsoft/terminal#9462
• you need to implement a COM server for this: https://github.com/microsoft/terminal/blob/main/src/host/proxy/ITerminalHandoff.idl
• in order to register your COM server with the OS you need to use sparse manifests: https://github.com/microsoft/AppModelSamples/tree/master/Samples/SparsePackages
• this is what needs to go into the manifest: https://github.com/microsoft/terminal/blob/eb7559733d3cc9062c7de610f3b95d9143099ca1/src/cascadia/CascadiaPackage/Package.appxmanifest#L77-L118 (a few lines below you can also see how to extend the context menu under Windows 11)

[ysc3839]

Here is a sample code for out-of-process COM register.