Implement proper dispose() methods for queueables.

- ValidatingBehaviour (was broken/incomplete!)
- UIBitmap
- UIComponent
- UITextField
@borrowed Style related owner/parent fields
Improved MacroUtils: don't generate empty methods

- re-enable MacroUtils.removeEmptyMethod, fix it
  by checking if there's at least a super class.

- Check if addMethod has already generated code.

- return constructor when looking for field `new`.
MacroUtils: Cast to IDisposable on untyped access.
More detailed debug code/line position info.