On WebSphere Liberty, the javax.validation package may be visible but
other javax.validation packages upon which it depends may not be
visible. This can lead to an incorrect assumption that the Bean
Validation API is available when, in fact, it is only partially
available.

Add an additional check for the availability of a class in the
javax.validation.bootstrap package to ensure that it's not just the
javax.validation package that's available.

Closes gh-10877