This commit removes the validation starter from the web and
webflux starters - we've reconsidered that choice since many were
not using this feature as part of their default web experience.
Thit commit also changes the default EL implementation for the
Jakarta implementation, aligning all servers on it and simplifying
dependency management (especially exclusions that were required
previously).
Closes gh-19550
Apply checkstyle rule to ensure that private and package private
classes do not have unnecessary public methods. Test classes have
also been unified as much as possible to use default scoped
inner-classes.
Closes gh-7316
