## What changes were proposed in this pull request?
Equi-height histogram is effective in cardinality estimation, and more accurate than basic column stats (min, max, ndv, etc) especially in skew distribution. So we need to support it.
For equi-height histogram, all buckets (intervals) have the same height (frequency).
In this PR, we use a two-step method to generate an equi-height histogram:
1. use `ApproximatePercentile` to get percentiles `p(0), p(1/n), p(2/n) ... p((n-1)/n), p(1)`;
2. construct range values of buckets, e.g. `[p(0), p(1/n)], [p(1/n), p(2/n)] ... [p((n-1)/n), p(1)]`, and use `ApproxCountDistinctForIntervals` to count ndv in each bucket. Each bucket is of the form: `(lowerBound, higherBound, ndv)`.
## How was this patch tested?
Added new test cases and modified some existing test cases.
Author: Zhenhua Wang <wangzhenhua@huawei.com>
Author: Zhenhua Wang <wzh_zju@163.com>
Closes#19479 from wzhfy/generate_histogram.
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