Small optimization in rounding

Instead of doing a multiplication here, we can just check if the
remainder is zero. This matters a bit more for TimeDuration and
RoundNumberToIncrementAsIfPositive, because we avoid a BigInt
multiplication.

UPSTREAM_COMMIT=407adc9e221eecb97e4db1c7b2b8e2b41cbea29a

Author: ptomato

lib/timeduration.ts

@@ -132,7 +132,7 @@ export class TimeDuration {
     const r2 = JSBI.add(r1, increment);
     const cmp = compare(abs(JSBI.multiply(remainder, TWO)), increment);
     const unsignedRoundingMode = GetUnsignedRoundingMode(mode, sign);
-    const rounded = JSBI.equal(abs(this.totalNs), r1)
+    const rounded = JSBI.equal(remainder, ZERO)
       ? r1
       : ApplyUnsignedRoundingMode(r1, r2, cmp, isEven(quotient), unsignedRoundingMode);
     const result = sign === 'positive' ? rounded : JSBI.unaryMinus(rounded);