DWDS error handling should align better with `vm_service`'s error handling

[elliette]

Context:

• Migrate all users of new Flutter SDKs to the new SDK DAPs Dart-Code/Dart-Code#4543
• [flutter_tools] Unexpected null value in AppInspector.jsEvaluate in dwds flutter/flutter#126362

DWDS doesn't always return an exception of type RPCError (defining in package:vm_service) when something goes wrong, which means that clients expecting an RPCError don't catch the exceptions thrown by DWDS.

We should make sure that DWDS returns semantic exceptions for all the API methods in chrome_proxy_service. This will require updating package:vm_service to expose all the error codes (including those currently defined in DDS and not exposed).

[elliette]

Note: error codes from DDS were exposed in dart-lang/sdk@66ded0c