Wrapper's isWrapperFor and unwrap methods both take a Class<?> target
but document that the target should be an interface. Prior to this
change, we were calling isWrapperFor with any Class<?> irrespective of
whether or not it was an interface. When using Oracle UCP each call
to isWrapperFor with an interface results in an exception stack trace
being logged.

This commit upates DataSourceUnwrapper to adhere to Wrapper's contract
by only calling isWrapperFor and unwrap with interfaces.

Fixes gh-24154