LOG4J2-1681 Changed visibility of indexed getter methods in SortedArrayStringMap from package-protected to public.

LOG4J2-1648 SPI interface for putting Object values in the ThreadContextMap (no end-user visible API yet)

LOG4J2-1226 Improve LogEvent serialization to handle non-serializable Messages and deserializing when required classes are missing.

LOG4J2-1663 Ensure SortedArrayStringMap can be serialized and deserialized without errors regardless of content

LOG4J2-1663 Ensure SortedArrayStringMap can be serialized and deserialized without errors regardless of content

This allows the compiler args configuration to be used for all child
POMS. This commit does not include compiler args for annotation
processing but I have experiments that do for experimenting with
generating different kinds of plugin cache files for all modules.

The parent POM does not compile anything, so it does not need to
configure the compiler. The configuration in the parent POM's plugin
management section is inherited by children.

The compiler plugin version is already defined in the plugin management
section.