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ARROW-11018: [Rust][DataFusion] Add support for column-level statistics, null count.

This adds extra statistics on the amount of nulls per column.

This is a step towards supporting more flexible cost based optimizations.

Second step is adding number distinct, min, max values. With that we can have a good estimate of selectivity of filters, supporting more cases in which we could apply optimizations such as reordering joins.

Notes

* It is a `Vec` to be in line with things like projections
* I think in memory / parquet (locally) it could be provided on read, for other datasources it might be useful to have support for something like `ANALYZE TABLE`.

FYI @andygrove this is one step for more flexible CBO for joins combined with filters.

Closes #8998 from Dandandan/null_count

Lead-authored-by: Heres, Daniel <danielheres@gmail.com>
Co-authored-by: Daniël Heres <danielheres@gmail.com>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>