Handle enum variants that conflict with EnumTypeWrapper methods

Eg
```
enum E {
    Name = 1;
    Value = 2;
}
```
Currently, it generates working python code, but broken stubs.
In python code - this all works.
```
from test_pb2 import E, Name, Value
assert Name == 1
assert Value == 2
assert E.Name(1) == 'Name'
assert E.Value('Name') == 1
```