feat(spec): add new specJS selector (#8936)

This selector always returns the same JavaScript
object unless it really changes.

Before this change it customary to call
specJson().toJS() which always resulted
in transformation operation and new JavaScript
object.

Refs #8606

src/core/plugins/spec/actions.js

@@ -238,7 +238,7 @@ const debResolveSubtrees = debounce(async () => {
       }
     }, Promise.resolve({
       resultMap: (specSelectors.specResolvedSubtree([]) || Map()).toJS(),
-      specWithCurrentSubtrees: specSelectors.specJson().toJS()
+      specWithCurrentSubtrees: specSelectors.specJS()
     }))
 
     delete requestBatch.system

src/core/plugins/spec/selectors.js

@@ -38,6 +38,11 @@ export const specJson = createSelector(
   spec => spec.get("json", Map())
 )
 
+export const specJS = createSelector(
+  specJson,
+  (spec) => spec.toJS()
+)
+
 export const specResolved = createSelector(
   state,
   spec => spec.get("resolved", Map())