Add Lint rules warning against accessing the Dispatchers object or creating CoroutineScope without a DispatcherProvider

[RBusarow]

Any access to the Dispatchers object breaks tests. This happens if we create a CoroutineScope without giving it a DispatcherProvider, or if we hard-code stuff like this:

class SomeClass {

  // We can still use `.dispatcherProvider` with this coroutineScope,
  // but it always returns a default implementation
  val coroutineScope = CoroutineScope(Job() + Dispatchers.Main)

  // This obviously accesses a hard-coded dispatcher
  fun foo() = coroutineScope.launch(Dispatchers.Default) { ... }
}

This is relatively easy to catch with Lint rules, but adding that rule to the main artifact will immediately create a warning for any code which has not been refactored.

Open Items

• Should a Lint rule go into its own artifact, effectively allowing the user to opt in by adding the dependency? Or should it just be published as part of the core artifact?