[Core] Use meaningful thread names (#1623)
[Core] Use meaningful thread names (#1623)

Before it was using the standard threadfactory, which
was naming threads like `pool-x-thread-y`. Now it is
`cucumber-runner-y-thread-x`. This better for logging to
 see which threads belong to cucumber and which are
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cucumber/cucumber-jvm,cucumber/cucumber-jvm,cucumber/cucumber-jvm,cucumber/cucumber-jvm,cucumber/cucumber-jvm