Increase logging for spring-messaging tests

A temporary measure related to intermittent CI build server failures.
Improve Javadoc for DatabasePopulator
Improve DataSourceInitializer Javadoc and implementation
Overhaul Javadoc for embedded database support
Support Class meta-annotation attributes with ASM

Prior to this commit, AnnotationAttributesReadingVisitor treated Class
annotation attributes as Strings instead of Classes. As a result,
look-ups for Class attributes in meta-annotations failed with an
IllegalArgumentException.

This commit fixes this issue by consistently treating Class attributes
as Classes in AnnotationAttributesReadingVisitor.

Issue: SPR-11557
Update TODOs for SPR-11574

Issue: SPR-11574
Detect ControllerAdvice beans in ancestor contexts as well

Issue: SPR-11570
Polishing
Polish Javadoc for embedded database support
Improve configurability of EmbeddedDatabaseBuilder

This commit improves the configurability of EmbeddedDatabaseBuilder by
exposing the following new configuration methods.

 - setDataSourceFactory(DataSourceFactory)
 - addScripts(String...)
 - setScriptEncoding(String)
 - setSeparator(String)
 - setCommentPrefix(String)
 - setBlockCommentStartDelimiter(String)
 - setBlockCommentEndDelimiter(String)
 - continueOnError(boolean)
 - ignoreFailedDrops(boolean)

If more fine grained control over the configuration of the embedded
database is required, users are recommended to use
EmbeddedDatabaseFactory with a ResourceDatabasePopulator and forego use
of the builder.

Issue: SPR-11410
Set DB_CLOSE_ON_EXIT=false in H2EmbeddedDbConfig

This commit sets the DB_CLOSE_ON_EXIT flag to false for embedded H2
databases loaded using H2EmbeddedDatabaseConfigurer (i.e., via Spring's
<jdbc:embedded-database /> XML namespace, EmbeddedDatabaseBuilder,
EmbeddedDatabaseFactory, and EmbeddedDatabaseFactoryBean).

Issue: SPR-11573