Consistently accept empty Content-Type header and empty character encoding

Issue: SPR-12173
(cherry picked from commit a1c0905)
ConfigurationClassParser avoids ImportBeanDefinitionRegistrar double scan

Issue: SPR-12334
QualifierAnnotationAutowireCandidateResolver calls BeanFactory.getType defensively

Issue: SPR-12191
(cherry picked from commit 73ce3b5)