Calcite engine. Avoid full index scans in case of null dynamic parameter

Currently, queries like:

SELECT * FROM tbl WHERE a >= ?

Should return no rows if dynamic parameter is null, but can be downgraded to full index scan in case table have index on column a (ASCENDING order, NULLS FIRST).

We should somehow analyse nulls in search bounds and return empty rows iterator for regular field conditions (`=`, `<`, '>`, etc). But also nulls should be processed as is in search bounds for conditions like `IS NULL`, `IS NOT NULL`, `IS NOT DISTINCT FROM` (the last one not supported currently).