Rename Closure V1 compatibility PolymerDomApi types for TypeScript ty…

…pes.

These interface types only exist for Closure compilation compatibility
between V1 and V2/3, but there's no reason to have them in our
TypeScript types.

- PolymerDomApi -> DomApi
- PolymerDomApi.ObserveHandle -> FlattenedNodesObserver

gen-tsd.json

@@ -12,7 +12,9 @@
     "../shadycss/custom-style-interface.d.ts"
   ],
   "renameTypes": {
-    "Polymer_PropertyEffects": "PropertyEffects"
+    "Polymer_PropertyEffects": "PropertyEffects",
+    "PolymerDomApi": "DomApi",
+    "PolymerDomApi.ObserveHandle": "FlattenedNodesObserver"
   },
   "autoImport": {
     "./interfaces": [