Ensure SystemUTCEpochNanoseconds never throws

Times outside of a range of about half a million years cannot be
represented by Temporal.Instant. Clamp the system time to that range so
that the operation is guaranteed not to throw, which is editorially the
cleanest solution. If your clock is 300,000 years off then Temporal is not
the biggest problem you will have, so this is not expected to come up in
practice.

See: #1424

Author: ptomato

lib/ecmascript.mjs

@@ -4352,7 +4352,7 @@ export const ES = ObjectAssign({}, ES2020, {
       const ms = Date.now();
       const result = bigInt(ms).multiply(1e6).plus(ns);
       ns = ms % 1e6;
-      return result;
+      return bigInt.min(NS_MAX, bigInt.max(NS_MIN, result));
     };
   })(),
   SystemTimeZone: () => {