Overhaul non-void JavaBean write method support

This change revisits the implementation of ExtendedBeanInfo, simplifying
the overall approach while also ensuring that ExtendedBeanInfo is fully
isolated from the BeanInfo instance it wraps. This includes any existing
PropertyDescriptors in the wrapped BeanInfo - along with being copied
locally into ExtendedBeanInfo, each property descriptor is now also
wrapped with our own new "simple" PropertyDescriptor variants that
bypass the soft/weak reference management that goes on in both
java.beans.PropertyDescriptor and java.beans.IndexedPropertyDescriptor,
maintaining hard references to methods and bean classes instead. This
ensures that changes we make to property descriptors, e.g. adding write
methods, do not cause subtle conflicts during garbage collection (as was
reported and reproduced in SPR-9702).

Eliminating soft/weak reference management means that we must take extra
care to ensure that we do not cause ClassLoader leaks by maintaining
hard references to methods, and therefore transitively to the
ClassLoader in which the bean class was loaded. The forthcoming
SPR-10028 addresses this aspect.

See the updated ExtendedBeanInfo Javadoc for further details.

Issue: SPR-8079, SPR-8175, SPR-8347, SPR-8432, SPR-8491, SPR-8522,
       SPR-8806, SPR-8931, SPR-8937, SPR-8949, SPR-9007, SPR-9059,
       SPR-9414, SPR-9453, SPR-9542, SPR-9584, SPR-9677, SPR-9702,
       SPR-9723, SPR-9943, SPR-9978, SPR-10028, SPR-10029

Author: cbeams