Auto merge of #18176 - rtbo:perf_observer_buffered, r=ferjm

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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components/script/dom/performanceentry.rs

@@ -51,6 +51,10 @@ impl PerformanceEntry {
     pub fn name(&self) -> &DOMString {
         &self.name
     }
+
+    pub fn start_time(&self) -> f64 {
+        self.start_time
+    }
 }
 
 impl PerformanceEntryMethods for PerformanceEntry {