Externs Inference Warnings

[superstructor]

Steps to Reproduce

Compile a re-frame project (e.g. todomvc example) with shadow-cljs settings of:

:compiler-options {:infer-externs :all}

Actual Behavior

------ WARNING #228 - :infer-warning -------------------------------------------
 Resource: re_frame/interop.cljs:22:3
 Cannot infer target type in expression (. x -reagent$ratom$IReactiveAtom$)
--------------------------------------------------------------------------------

------ WARNING #229 - :infer-warning -------------------------------------------
 Resource: re_frame/interop.cljs:51:9
 Cannot infer target type in expression (. reactive-val -reagent$ratom$IReactiveAtom$)
--------------------------------------------------------------------------------

Desired Behavior

No warnings from re-frame code.

We are only responsible for 2 out of 234 inference warnings on the todomvc app but we may as well fix our part of it.

A previous commit fixed a similar warning.

shadow-cljs user guide has some tips on fixing externs warnings.