[generator] Mark abstract methods as [Obsolete] if needed.

[jpobst]

Fixes: #969

If you have a Java abstract method which is deprecated:

publicabstractclassExample {
@Deprecatedpublicabstractvoidm();
}

then the C# binding is not[Obsolete], and the *Invoker override is[Obsolete]:

// BindingpublicabstractpartialclassExample:Java.Lang.Object{[Register(…)]publicabstractvoidM();}internalpartialclassExampleInvoker:Example{[Obsolete]publicoverridevoidM()=> …
}

This state of affairs results in a CS0809 warning:

Error CS0809: Obsolete member 'ExampleInvoker.M()' overrides non-obsolete member 'Example.M()'

Expand the fix from #968 to apply to XAJavaInterop1 code generation.