Sql. Align implementations of average calculation (AVG)

We have Map/Reduce and Collocated algorithms of implementations for calculation average values.
At least for the DECIMAL type we have different implementations which can produce different precision/scale of results and value of results.

We need to do the following:
1) Check implementations of AVG for all types and align them, including resolving types of results.
2) The result type of AVG in the plan and the real result type after execution should be identical.

Points to start investigate:

1. ItAggregatesTest
2. AccumulatorsFactory
3. IgniteSqlFunctions#decimalDivide
4. MapReduceAggregates#createAvgAgg