Consider loosening InvocationEventHandler generic to Object

[carterkozak]

What happened?

Several of our handlers require a small slice of what is available on InvocationHandler:

• TracingInvocationEventHandler only uses java.reflect.Method.getName() for operation names
• MetricsInvocationEventHandler uses getStartTimeNanos() and getMethod()
• CompositeInvocationEventHandler uses no values from InvocationContnext, only a array of contexts.

What did you want to happen?

We should consider loosening InvocationEventHandler generic to Object from InvocationContext. CompositeInvocationEventHandler may implement InvocationEventHandler<Object[]> and avoid copying argument arrays, additional System.nanoTime calls, etc.