Mark symbols as obsolete

[badcel]

If an api is marked deprecated generate an obsolete attribute for it with the information since when it is obsolete.

Consider using custom attributes instead of the Microsoft ones for obsoleting or marking api with "since". This could allow a user to set which api version to use globally and if some api is called which is not active a warning / error can be emitted via integration library.

This would probably need support for generic attributes to add support via GObject integration for all libraries as an enum could be used as gemeric argument specifying the api sets. The enum can be manually written as a start.

Generic attributes are support starting with dotnet 7.