Port PR: Clear resolver jar entries cache after unpacking stubs (spring-attic#2165)

## Origin
Porting https://github.com/spring-attic/spring-cloud-contract/pull/2165 by @fstaudt

Fixes https://github.com/spring-attic/spring-cloud-contract/issues/2164

## Summary
Clears the resolver jar entries cache after unpacking stubs jars, preventing stale cache entries from causing incorrect behaviour in subsequent resolutions.