Reverse SPR-10402 change that caused 3.2.3 regression

SPR-10402 in Spring Framework 3.2.3 treated empty request parameter
values as missing values, if the empty value was turned into a null
by a PropertyEditor or Converter. This caused the regression.

Issue: SPR-10578, SPR-10402, SPR-10584
Add mvc: prefix to mapping samples in ref docs

Add 'mvc:' namespace prefix to 'mapping' and 'exclude-mapping' elements
in the reference documentation.

Issue: SPR-10670
Add HTTP method to RequestDataValueProcessor method

Issue: SPR-10041, SPR-10652
Add accept(String) method to mock request builder

Issue: SPR-10390
Add getResult/hasResult methods to DeferredResult

Issue: SPR-10603
Fix getters to match setters in RMHA

Issue: SPR-10519
Inject @Configuration BeanFactory before autowire

Add EnhancedConfigurationBeanPostProcessor to inject the BeanFactory
into EnhancedConfiguration classes before the
AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues method
is called.

Prior to this commit it was possible for @Autowire in a @Configuration
class to invoke an enhanced configuration class method before the
BeanFactory was injected. This is due to the fact that the
AutowiredAnnotationBeanPostProcessor was called before
AbstractAutowireCapableBeanFactory.invokeAwareMethods().

Issue: SPR-10668
Skip abstract beans in getBeansWithAnnotation()

Update BeanFactory.getBeansWithAnnotation() to skip any abstract
bean definitions.

Issue: SPR-10663
Use 'Integer' not 'int' in queryForObject  docs

Update queryForObject calls in the JDBC reference documentation to
use 'Integer.class' rather than the unsupported 'int.class'.

Issue: SPR-10651
SimpleKeyGenerator to replace DefaultKeyGenerator

Introduce new SimpleKeyGenerator class to supersede DefaultKeyGenerator.
Unlike DefaultKeyGenerator, no collisions will occur with the keys
generated by SimpleKeyGenerator as the full parameter values are
considered within the SimpleKey.equals(...) method.

The SimpleKeyGenerator is now the default class used when no explicit
generator is configured.

Issue: SPR-10237