problems with type inference in the face of the any type

[faassen]

When you create a repeatingAccessor or a subForm accessor and you set their type to RepeatingFormAccessor<any,any> or SubFormAccessor<any, any>, typescript loses the ability to recognize that a field exists deeper down in an indexed accessor. It doesn't seem to happen when a repeating/sub form isn't in play.

This may await a big incompatible rework where we do as MST does and make sub/repeating forms declare their MST type just like we ask for forms.