Index Condition Pushdown for k-ANN graph searches

After the implementation of MDEV-33408:

Modify the basic graph search algorithm to support index condition pushdown. That is, only add nodes to the candidate result set that pass the WHERE clause.

This will allow queries of the form:

SELECT *

FROM table

WHERE cond(table.column) == true

ORDER BY VEC_DISTANCE(table.emb, target_vec)

LIMIT 10

to take advantage of the index.

This will have the following edge cases:

• What if none of the neighbors of the upper layer pass the where clause?
• What if none of the neighbors in the search pass the where clause, but if we had only considered nodes that did pass (nodes that were never explored in this search), we would have found a valid result set.