Always supply test class to ContextLoaders in TCF

Prior to this commit, the following methods in ContextLoaderUtils
treated a composed @ContextConfiguration annotation (i.e., a custom
annotation that is meta-annotated with @ContextConfiguration) as the
"declaring class" instead of the actual test class.

- resolveContextConfigurationAttributes()
- resolveContextHierarchyAttributes()

As a consequence, if @ContextConfiguration is used as a
meta-annotation, the meta-annotated class is stored as the
"declaringClass" in ContextConfigurationAttributes. Thus, when a
ContextLoader (or SmartContextLoader) attempts to detect default
resource locations or configuration classes, it does so for the
composed annotation class instead of for the declaring test class.

This commit ensures that ContextLoaders are supplied the declaring test
class instead of the composed annotation class in such use cases.

Issue: SPR-11455
Merge changes from sbrannen/SPR-11455

* SPR-11455:
  Always supply test class to ContextLoaders in TCF