This allows for go-to-def on the a let field to resolve to the definition
of the base class. This is kind of like how C++ works with go-to-def
from use->def->decl, with the decl in this case being the base definition
of the field.
Depends on D134259
SMRange is defined as half-open so contains here feels off. closureContains would be more accurate but may not be too specialized. containsOrLimit would be more direct.
I'm worries that this could be hiding off-by-one issues.
(I also appreciate that this is a pure move and we could look at follow on that is more mechanical)