…and accessor interfaces to a generic type.

If we don't do this then the result from getInterfaces and getGenericInterfaces won't be aligned which can cause issues when application/framework code inspects the class using reflection. Normally this sort of thing is managed by the Java compiler, but since we're modifying things at the bytecode level we have to manage this ourselves.

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.3.4

Oracle's Java Virtual Machine implementation does not check the well-formedness of the signatures described in this subsection during loading or linking. Instead, these checks are deferred until the signatures are used by reflective methods, as specified in the API of Class and members of java.lang.reflect. Future versions of a Java Virtual Machine implementation may be required to perform some or all of these checks during loading or linking