The `FixedBackOffPolicy` and `ExponentialBackOffPolicy` have now overloaded
setters for `Supplier` of value.
The XML parser relies on the Java Bean specification and cannot determine
the proper setter by type.
Looks like it is just resolved by name and there is no guarantee which one
will win
* Add inner `FixedBackOffPolicy` and `ExponentialBackOffPolicy` adapters
to expose `*Simple` setters for the values we get from the XML configuration
b7dd7d1379