[Variant] impl `PartialEq` for `VariantArray`

[friendlymatthew]

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

A VariantArray represents a list of Variant values. While it's internal layout is columnar, this detail is largely irrelevant to end users.

Currently, Variant impls PartialEq, but VariantArray does not. This makes it cumbersome to compare 2 arrays of variants for equality in user code:

https://github.com/datafusion-contrib/datafusion-variant/blob/8081efc03ca6f3199a40dfbf0f9133e43adaaedd/src/shared.rs#L131-L165

Describe the solution you'd like

impl PartialEq for VariantArray

Additional context

This feature is motivated by datafusion-variant, a higher-level library that integrates with Datafusion through a series of udfs

Related: #8609

[Weijun-H]

This issue can be easily resolved after #8612 merged

[alamb]

label_issue.py automatically added labels {'parquet-variant'} from #8627