Spring Update package-info for CGLIB fork

Since we now maintain a complete fork of CGLIB, we should consider if we want to introduce package-info files for every package.

At the very least, we should update our existing package-info files to reflect the status quo.

• /spring-core/src/main/java/org/springframework/cglib/package-info.java
• /spring-core/src/main/java/org/springframework/cglib/beans/package-info.java
• /spring-core/src/main/java/org/springframework/cglib/core/package-info.java
• /spring-core/src/main/java/org/springframework/cglib/proxy/package-info.java