Unintercepted JS types/objects should be intercepted as some Dart Interceptor type

[srujzs]

We currently have Interceptors in the web compilers to represent JS types and objects e.g. JavaScriptObject, Native classes, etc. However, these don't seem to fully capture all possible things in JS that you can operate. For example, the Symbol class doesn't seem to have a target interceptor. There was also discussion on whether or not BigInt is properly intercepted. The lack of an intercepted type means interop with these types/objects proves painful, especially when we move to the model of exposing JavaScriptObject as the catch-all for all the types/objects we want to expose to users with extension types. Collections are also affected e.g. lack of hashCode. We should distinguish between the set of unintercepted things and determine where in the Interceptor hierarchy they should exist.