Argument Clinic: Better internal implementation for @getter and @setter

[corona10]

Even though we successed to provide @getter and @setter features from #112205
The current internal implementation is full of hacky workaround.

We need to improve the internal implementation for better generated C codes and maintenance.
@erlend-aasland wrote some ideas for this: #112205 (comment)

[corona10]

See also: #113160 (comment)

[erlend-aasland]

Thanks for creating this issue, Donghee. See #112205 (comment) for more info.