Prevent incorrect ImportAware metdata injection

Update ImportRegistry to track all import registrations that occur
against an importing class (rather than just keeping the last). In
addition, prune imported classes from the registry when a configuration
class is removed during the REGISTER_BEAN ConfigurationPhase.

This update prevents incorrect metadata from being injected into an
ImportAware class which is imported twice by different configurations
classes (when one of the configuration classes will be ultimately skipped
due to a @Condition).

Issue: SPR-12128
Update the what's new section
Add mention of ResponseBodyAdvice
Add section on building controller links from views
Update reference documentation for JSONP support

Issue: SPR-12113
Transform absolute links in ResourceTransformers

Prior to this change, ResourceTransformers that transformed resources by
updating the links to other resources, worked only if links were
relative to the resource being transformed.
For example, when the CssLinkResourceTransformer rewrote links within
a "main.css" resource, only links such as "../css/other.css" were
rewritten.

Using relative links is a recommended approach, because it's totally
independent from the application servlet path, context path, mappings...

This change allows absolute links to be rewritten by those Transformers,
provided those links are accurate and point to existing resources.

Issue: SPR-12137
ImportRegistry as a package-visible top-level interface which can easily be shared within the package

Issue: SPR-12128
Cache.get(key, type) explicitly defines an IllegalStateException in case of a type mismatch

Issue: SPR-12145
Rename test class to match name of class being tested
Update reference
Test for actual HttpInvokerProxyFactoryBean usage with plain FactoryBean return type

Issue: SPR-12141
CachingConnectionFactory proceeds to physicalClose in case of logicalClose exceptions

Issue: SPR-12148
Refactored support for @Order on @Bean methods as well as @Priority handling

Issue: SPR-11310
Issue: SPR-10548
Polishing
Polishing
Polishing