[DISCUSSION] Conditional Utf8View support for downstream projects

### Is your feature request related to a problem or challenge?

Datafusion Comet encountered a migration issue when upgrading to DataFusion 49, caused by https://github.com/apache/datafusion/pull/16290
which introduces Utf8View and replaces Utf8 for `md5` function.

Although the runtime behavior is mostly controlled via configuration parameters added in [PR #16809](https://github.com/apache/datafusion/pull/16809) we found that several function signatures have already been hardcoded to Utf8View.

Specifically for Comet project the `Utf8View` support is still in progress and hardcoding `Utf8View` makes migrations harder, in this particular case we do a unnecessary cast back to `Utf8`

It would be great to get more flexible support for `Utf8View` in DataFusion, ideally in a conditional or opt-in manner, and particularly in builtin functions where it is not feasible to access the `SessionContext` and make a return type by runtime configuration.

Maybe we can think of `features` to build the DataFusion with or without Utf8View?

Appreciate your thoughts

Comet migration PR https://github.com/apache/datafusion-comet/pull/2040
Related to https://github.com/apache/datafusion/issues/16235

@alamb @andygrove @mbutrovich @zhuqi-lucas

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by reading DataFusion PRs #16290 and #16809, the related issue #16235, and the DataFusion Comet migration PR #2040 to understand the Utf8View compatibility problem. The issue has no agreed solution or named files and tests; done would require a decided conditional or opt-in design and an implementation scope that downstream projects can use.

Written by the indexing model from the issue text.