Previously, AspectJ would find META-INF/aop.xml almost as soon as
the jar was launched, and before LaunchedURLClassLoader had been
created. This meant that AspectJ would attempt to load aspects listed
in META-INF/aop.xml but that were package in BOOT-INF/classes and,
therefore, could not be loaded.

This commit updates the Repackager so that a META-INF/aop.xml file
is moved into BOOT-INF/classes. This ensures that it isn't visible
to the app class loader so it won't be loaded to early. It will
now be loaded by LaunchedURLClassLoader which can also load the
compiled aspects that aop.xml references.

Closes gh-7587