Add `SkipIndex` in SortedNumericDocValuesSetQuery

### Description

`SkipIndex` is introduced in #13449, which is primarily utilized in range query like `SortedSetDocValuesRangeQuery` and `SortedNumericDocValuesRangeQuery`. I'm wondering if we could use it in `SortedNumericDocValuesSetQuery`.

Start by reading SortedNumericDocValuesSetQuery and the SkipIndex introduction in issue #13449, then compare how SkipIndex is used by SortedSetDocValuesRangeQuery and SortedNumericDocValuesRangeQuery. Determine whether the set query can use the same optimization and define completion by adding that support with coverage for the relevant query behavior.

Written by the indexing model from the issue text.