Fail workflow task on illegal calls in Workflow.await

[Quinn-With-Two-Ns]

Is your feature request related to a problem? Please describe.

Workflow.await is expected to be idempotent, so it is not allowed to make any calls to mutate workflow state like start an activity. If we detect any such call we should fail the workflow task since it indicates a bug in the workflow implementation.

boolean activityExecuted = Workflow.await(Duration.ofSeconds(5), () -> {
    activity.doSomething();
    return true;
});