Follow up on the removal of `update` and `merge` in `Accumulator`

[jimexist]

I think it would be a good idea as a follow on PR to update these implementations to avoid the use of ScalarValue.

I'll try find some time this week to do it (I need some coding time :) -- lots of reviewing so far)

Originally posted by @alamb in #1582 (comment)

[alamb]

Basically the idea here would be to rewrite the implementations that use ScalarValue to directly use the appriate arrow compute kernels: https://docs.rs/arrow/7.0.0/arrow/compute/index.html

[Weijun-H]

This issue can be closed, because all parts are refactored.

[alamb]

Thank you @Weijun-H