Begin migration to 'aspectj' locale for compiler messages

Begin migration to 'aspectj' locale for compiler messages

Renamed messages.properties to messages_aspectj.properties and moved to
a path identical with the Eclipse original resource file. Therefore, it
is now just treated as a localised version of it.

The new jdtcore-for-aspectj.jar already contains logic to use the new
locale. Hence, BuildArgParser no longer needs the static block to
initialise its own resource bundle, Eclipse JDT will automatically pick
it up.

The version string was also updated to the new Eclipse merge commit
hash + date + "Java16".

TODO: Strip down properties file in order to only contain delta to
Eclipse.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>