fix(ecmascript): `Math.round` only exact half ties (#26150)

[ECMA-262 §21.3.2.29, `Math.round`](https://tc39.es/ecma262/multipage/numbers-and-dates.html#sec-math.round).

- If `0 < n < 0.5`, return `+0`.
- If `-0.5 ≤ n < -0`, return `-0`.
- Otherwise choose the closest integer, preferring `+∞` only for an actual tie.