Add keep rule for kotlin.coroutines.Continuation

[mkj-gram]

I am unsure if the factory that checks for suspend functions relies on the name. If not, and the library do not need the name or location, this could be -keep,allowobfuscation instead.

[JakeWharton]

Sorry I missed this. We do not rely on the name so we can allow obfuscation. Also you'll need to rebase since Christoffer also sent a PR to add a rule.

The check for coroutines is the very last attempt to match a method signature so we compare against a class literal which has a try/catch:

try {
  if (Utils.getRawType(parameterType) == Continuation.class) {
    isKotlinSuspendFunction = true;
    return null;
  }
} catch (NoClassDefFoundError ignored) {
}
throw parameterError(method, p, "No Retrofit annotation found.");

[mkj-gram]

I rebased (I think) and also allowed for obfuscation and shrinking.

[JakeWharton]

Thanks!

[Simay15]

android.enableR8.fullMode=true