Revert "Refactor JSNumber.toDart and Object.toJS" (flutter#43286)

Reverts flutter/engine#43149

Reason for reverting: Broke the roll into the framework.

Author: srujzs

lib/web_ui/lib/src/engine/canvaskit/canvaskit_api.dart

@@ -205,10 +205,10 @@ Future<Uint8List> readChunked(HttpFetchPayload payload, int contentLength, WebOn
   int position = 0;
   int cumulativeBytesLoaded = 0;
   await payload.read<JSUint8Array1>((JSUint8Array1 chunk) {
-    cumulativeBytesLoaded += chunk.length.toDartInt;
+    cumulativeBytesLoaded += chunk.length.toDart.toInt();
     chunkCallback(cumulativeBytesLoaded, contentLength);
     result.set(chunk, position.toJS);
-    position += chunk.length.toDartInt;
+    position += chunk.length.toDart.toInt();
   });
   return result.toDart;
 }

lib/web_ui/lib/src/engine/canvaskit/image.dart

@@ -312,7 +312,7 @@ extension JsFlutterConfigurationExtension on JsFlutterConfiguration {
 
   @JS('canvasKitMaximumSurfaces')
   external JSNumber? get _canvasKitMaximumSurfaces;
-  double? get canvasKitMaximumSurfaces => _canvasKitMaximumSurfaces?.toDartDouble;
+  double? get canvasKitMaximumSurfaces => _canvasKitMaximumSurfaces?.toDart;
 
   @JS('debugShowSemanticsNodes')
   external JSBoolean? get _debugShowSemanticsNodes;