Refactor `ConfigurationPropertiesBindingPostProcessor` to allow JSR-303
validation on `@ConfigurationProperties` defined at the `@Bean` method
level.
JSR-303 validation is now applied when a JSR-303 implementation is
available and `@Validated` is present on either the configuration
properties class itself or the `@Bean` method that creates it.
Standard Spring validation is also supported using a validator bean
named `configurationPropertiesValidator`, or by having the configuration
properties implement `Validator`.
The commit also consolidates tests into a single location.
Fixes gh-10803
1d83e87bcd