Add compiler plugin support for `cumSum`

[zaleslaw]

https://github.com/Kotlin/dataframe/blob/master/core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/cumSum.kt

[zaleslaw]

Closed in #1077

[zaleslaw]

@Jolanrensen before I've started to implement this ticket, I've discovered, that cumSum is missing in Aggregators.kt and also there is no cumSumFor and cumSumOf for GroupBy section...could you please add them, when you will finish the Statistics