[C++] Improve Decimal32 conversion from Real

[zeroshade]

Describe the enhancement requested

Currently, to avoid precision and rounding differences, we unconditionally push FromPositiveReal for Decimal32 to use the approximate algorithm. This is because the iterative multiply/divide paths result in losing a few bits that causes an off-by-one issue with Decimal32 values at the edges (or close to) the max precision of it.

A possible solution might be to convert to Decimal64 and then convert back down to Decimal32 afterwards, though it might still have rounding issues.

Overall, while using the approx algorithm isn't bad, we can probably do better and should look into improving it.

Component(s)

C++