Previously, the WebFlux starter declared direct dependencies on Hibernate Validator
and the Jakarta EE validation API. This meant that it required two exclusions to
exclude validation from a reactive web application that did not need it.

This commit updates the WebFlux starter to get its validation dependencies via a
dependency on the validation starter. This allows validation to be excluded
using a single exclusion. The EL dependency from the validation starter has
been excluded to allow the EL implementation from the underlying container
starter to continue to be used instead.

See gh-16593