More test cases for Drop

[YoshikiTakashima]

As per request from @danielsn, I'm adding more test cases for the Drop trait.

The following cases are going to be added.

• Enum drop. Construct and drop an enum. Assert the following:
  • That either one of the drop function will be called
  • That both are not called
• Move across the sync channel. Check drop side effect
• Move Closure. Check that drop is called when object is inside move closure.
• Rc<RefCell<T>>: Common pattern for nested shared inner mutability. Drop and mutation effects should be asserted.