Simplify predicate concatenation in JpqlQueryBuilder.and(List)

[JunggiKim]

JpqlQueryBuilder.and(List) combines predicates by repeatedly calling Predicate.and(Predicate), and each of those calls flattens everything accumulated so far into a new list, so the element copies are quadratic in the number of predicates. AndPredicate.of(List) already flattens a list in one pass and or(List), directly below, already delegates to OrPredicate.of(List), so and(List) now delegates the same way. The empty and single-element cases stay explicit to keep the returned instance the same as before.

The only caller is KeysetScrollSpecification, where the list holds one predicate per keyset sort key; in the queries the tests generate that is one to four predicates. One thing does change for input that caller never produces: a null next to another predicate used to be dropped, or to fail inside List.of, and now throws when the predicate is rendered.

The added tests pass against the previous implementation too, and the module test suite passes before and after.

• You have read the Spring Data contribution guidelines.
• You use the code formatters provided here and have them applied to your changes. Don't submit any formatting related changes.
• You submit test cases (unit or integration tests) that back your changes.
• You added yourself as author in the headers of the classes you touched. Amend the date range in the Apache license header if needed. For new types, add the license header (copy from another file and set the current year only).