feat: add array_first higher-order array function (#23267)

## Which issue does this PR close?

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No dedicated tracking issue; this adds a single self-contained
higher-order array function. Happy to file one if preferred.

## Rationale for this change

DataFusion already provides higher-order array functions such as
`array_any_match`, `array_filter`, and `array_transform`, but there is
no direct way to retrieve the *first* element of an array that satisfies
a predicate. Today this requires `array_filter` followed by
`array_element(..., 1)`, which materializes an intermediate filtered
array. `array_first` expresses this directly and rounds out the set of
lambda-based array functions.

## What changes are included in this PR?

- New higher-order function `array_first(array, predicate)` (alias
`list_first`) in `datafusion-functions-nested`, returning the first
element for which the lambda predicate returns `true`:
  - returns `null` when the array is empty or no element matches;
- a predicate that evaluates to `null` for an element is treated as not
matching;
  - a matched element that is itself `null` is returned as `null`.
- Implemented as a `HigherOrderUDFImpl` following the existing
array-lambda functions, including the standard fast paths (fully-null
input) and correct handling of sliced lists, null sublists, and captured
outer columns.
- Registration in `functions-nested` (`expr_fn` re-export and the
default higher-order function list).
- Unit tests, sqllogictest coverage, and regenerated SQL function
documentation.

## Are these changes tested?

Yes:
- Unit tests in `array_first.rs` covering match/no-match, empty and null
arrays, null-predicate handling, matched-null elements, sliced lists,
captured outer columns, and non-primitive element types.
- sqllogictest cases in `test_files/array/array_first.slt`, including
`LargeList` and the `list_first` alias.

## Are there any user-facing changes?

Yes. A new array function `array_first` (alias `list_first`) is
available in SQL, with generated documentation under the Array Functions
section. There are no breaking changes to existing public APIs.

Author: EdsonPetry