1853: Introduce FromSource trait r=matklad a=viorina
The idea is to provide an ability to get HIR from AST in a more general way than it's possible using `source_binder`.
It also could help with #1622 fixing.
Co-authored-by: Ekaterina Babshukova <ekaterina.babshukova@yandex.ru>
cd9b222ba0