Current variables exposed by layouts do not resolve the field variable.
Variables exposed in the case of a template widget type could also be useful when defining EL expressions for widget mode resolution or for widget properties resolution.
=> need to expose:
- field variables like the template widget type does
- xpath like variables to be able to use the current doc path
- widget controls and properties
Also there is a mix between the different ways to expose variables at build time and render time, need to check if this can be cleaned up as the layout system produces a lot of UIAliasHolder tags (and it may produce less, or optimize what's exposed to the context, see for instance fix for