Remove Introspected from MyValidatorBean example

[jeremyg484]

The docs are updated to no longer show the use of the @Introspected annotation on the MyValidatorBean example, as it cannot successfully be used on a validator that is a managed bean with dependencies.

DefaultInternalConstraintValidatorFactory is updated to include the exception cause in the stack trace when a validator cannot be initialized.

The CustomMessageConstraint2Validator test class for CustomConstraintsSpec is updated to include a dependency that must successfully be injected in order to verify that this works as long as the validator is not also Introspected.

Resolves #258

Note For Reviewers:

An alternative approach that I considered is to change this lookup algorithm in DefaultInternalConstraintValidatorFactory to instead look for a bean first before looking for the introspection. Something such as:

entry = Optional.ofNullable(instantiateConstraintValidatorEntryOfBeanRegistration(type))
                .or(() -> beanIntrospector.findIntrospection(type)
                .map(this::instantiateConstraintValidatorEntry)).orElseThrow();

This allows the existing example with both @Singleton and @Introspected to still work when an injected dependency is required in the constructor...but I am of the opinion that it is incorrect in the first place to have @Introspected on a managed bean. The upside to doing that would be that users' 3.x apps that followed the example won't break when upgrading to 4.x, but this seems acceptable as a breaking change in the major version.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud