[BUGFIX beta] Avoid extending a view for every {{each}}.

Replaces #9670.

I believe that in general #9670 is absolutely the right way forward for things like `MODEL_FACTORY_INJECTIONS`, but it is not needed for this localized use case.  I'd rather get this into beta without adding new API surface, and then we can figure out the long term fix for factory injections.

/cc @stefanpenner @ebryn @mixonic