[XC] Infer x:DataType from BindingContext or BindingExtension.Source

[simonrozsival]

In certain scenarios, XamlC should be able to infer the x:DataType based on the value passed to BindingContext on any XAML element or to Source on BindingExtension elements:

• {StaticResource X} - in the case when X is defined in the same XAML document
• {x:Static Y}
• {x:Reference Z}
• {Binding W} - when the binding is compiled
• {Binding Source={RelativeSource U}}:
  • Self - when the elemet to which the binding is set is statically known
  • FindAncestor
  • FindAncestorBindingContext - when the ancestor and the type of the binding context can be statically resolved
  • TemplatedParent - when the templated parent can be statically resolved

Explicitly declared x:DataType should always take precedence over the inferred type. In the case when there is a mismatch, we should consider emitting a warning.

Are there any other cases which we could infer?

/cc @StephaneDelcroix