[Variant] casting functions are confusingly named

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
We have two functions that are inverses of each other that are confusingly named;

• cast_to_variant which casts arrow arrays to variant
• variant_to_arrow which casts variants to arrow arrays

Further adding to the confusion is that we have modules named arrow_to_variant which doesn't contain the casting kernel

Describe the solution you'd like
I would like the names to be consistent

Describe alternatives you've considered
I propose changing the names of the casting functions to be more explicit:

• cast_arrow_to_variant
• cast_variant_to_arrow

And leaving the conversion code in the modules arrow_to_variant and variant_to_arrow

Additional context
Came up with conversation with @scovich on

• 509d432#r2393067849

[alamb]

Actually, I am going crazy -- there is no variant_to_arrow, instaed that is done by variant_get

I will make this clearer in docs

[alamb]

label_issue.py automatically added labels {'parquet'} from #8536

[alamb]

label_issue.py automatically added labels {'parquet-variant'} from #8536