JetStream Clone

This is a clone from the upstream (webkit repository)[https://github.com/WebKit/WebKit/tree/main/Websites/browserbench.org/JetStream2.2]

It contains additional changes to help with investigation:

• Added --help command line support
• Additional performance mark and measure calls
• Use performance.mark instead of Date.now
• Additional URL params to configure iterationCount and worstCaseCount
• Pass iterationCount Benchmark.validate, needed for UniPoker
• Print Score and time for metrics
• Customized file-prefetcher to support runner WorkerTests in d8