Moving class doesn't move class decorator.

[climbus]

Moving class doesn't move class decorator.

Steps to reproduce the behavior:

1. Code before refactoring:

mod1.py

@dataclass
class AClass:
    pass

class BClass:
    pass

2. Move AClass to mod2.py

3. Expected code after refactoring:
   mod1.py

class BClass:
    pass

mod2.py

@dataclass
class AClass:
    pass

4. Describe the error or unexpected result that you are getting
   mod1.py

@dataclass
class BClass:
    pass

mod2.py

class AClass:
    pass

Editor information (please complete the following information):

• Project Python version: 3.8.8
• Rope Python version: 3.8.8
• Rope version: 0.21.0
• Text editor/IDE and version: reproduced in tests