fix(lib): add PerformanceObserver and PerformanceObserverEntryList types

[bartlomieju]

PerformanceObserver and PerformanceObserverEntryList exist at runtime in
Deno but were never declared in the default libs — only lib.webworker.d.ts
declares them, and the deno.window lib doesn't load it. As a result:

const obs = new PerformanceObserver(
  (list: PerformanceObserverEntryList) => { // TS2749 before this change
    for (const e of list.getEntries()) console.log(e.name);
  },
);
obs.observe({ entryTypes: ["measure"] });

PerformanceObserverEntryList used as a type errored with TS2749
("'PerformanceObserverEntryList' refers to a value, but is being used as a type
here"), even though the value exists at runtime.

This adds the PerformanceObserver, PerformanceObserverEntryList, and
PerformanceObserverCallback declarations to lib.deno.shared_globals.d.ts
next to the existing Performance / PerformanceEntry / PerformanceMark /
PerformanceMeasure ones, so both are usable as values and types in Deno code.

---

Part of the broader effort to drop Deno's forked TypeScript; see #35621 for context and the overall plan.