Introduce ActiveProfilesResolver in the TCF

Prior to this commit, the active bean definition profiles to use when
loading an ApplicationContext for tests could only be configured
declaratively (i.e., via hard-coded values supplied to the 'value' or
'profiles' attribute of @ActiveProfiles).

This commit makes it possible to programmatically configure active bean
definition profiles in tests via a new ActiveProfileResolver interface.
Custom resolvers can be registered via a new 'resolver' attribute
introduced in @ActiveProfiles.

Overview of changes:

 - Introduced a new ActiveProfilesResolver API.
 - Added a 'resolver' attribute to @ActiveProfiles.
 - Updated ContextLoaderUtils.resolveActiveProfiles() to support
   ActiveProfilesResolvers.
 - Documented these new features in the reference manual.
 - Added new content to the reference manual regarding the
   'inheritProfiles' attribute of @ActiveProfiles
 - Removed the use of <lineannotation> Docbook markup in the testing
   chapter of the reference manual for Java code examples in order to
   allow comments to have proper syntax highlighting in the generated
   HTML and PDF.

Issue: SPR-10338
Merge from sbrannen/SPR-10338

* SPR-10338:
  Introduce ActiveProfilesResolver in the TCF