PerformanceObserverInit.buffered
Per #18108, add `buffered` flag in the `PerformanceObserverInit` dict.
Per W3C spec, when `buffered` is set, `PerformanceObserver.observe()` method adds the entries buffered in the `Performance` instance into the observer's entry buffer.
One step is the implementation of the [filter by name and type](https://w3c.github.io/performance-timeline/#filter-buffer-by-name-and-type) algorithm. Don't think that the sort operation is useful in this case, but the spec states that this algorithm is to be used.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#18108
- [X] These changes do not require tests (yet) because the timeline API is not powered.
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