classloader caching - instance of classloader cache is shared

Ensured the instance of classloader cache is shared in standard mode, e.g. without even classloader caching enabled. Originally, I let the DefaultScriptCompilationHandler have its own instance of classloader cache to lower any possible impact.

+review REVIEW-5219
classloader caching - added executer.withClassLoadingCaching

Reworked the coverage and pushed more complexity onto the executor. Much better now, thanks for review!!!

+review REVIEW-5219