Fix ROUND() returning incorrect results for edge cases

[sviscaino]

ROUND(double, integer) and ROUND(real, integer) are returning wrong results for edge cases:

• if the first argument does not fit in a long: currently ROUND(double'1e100', 0) returns 9223372036854800000
• if the second argument is too big (around ~20), which makes Math.round(num*factor) overflow: currently ROUND(double'1', 20) returns 0.092233720368548

Instead, we use this approach by scaling down a BigDecimal.

Test plan -
mvn -Dtest="TestMathFunctions" test

== RELEASE NOTES ==

General Changes
* Fix :func:`round` returning incorrect results for edge cases

[arunthirupathi]

This caused a huge performance regression on the 0.278 rollout for some queries.
Same query profiled on the 0.277

Regressed query profiled on the 0.278

The query had a large map<int, float> and it was casting it to map<bigint, bigint> and it regressed a lot.