Align cast logic for from/to_decimal for variant to cast kernel

[klion26]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Related to #8982 for from/to_decimals

Describe the solution you'd like

Extract the logic in arrow-cast and reuse in arrow-cast and parquet-variant

Describe alternatives you've considered

Additional context

[klion26]

take

[alamb]

label_issue.py automatically added labels {'arrow'} from #9689

[alamb]

label_issue.py automatically added labels {'parquet-variant'} from #9689