jdbc: metadata: provide nullsAreSorted*()

[Totktonada]

DatabaseMetaData.

The following methods should return the following values:

• nullsAreSortedAtEnd -- false
• nullsAreSortedAtStart -- false
• nullsAreSortedHigh -- false
• nullsAreSortedLow -- true

Also we need to cover these methods with a test.

How to check:

box.cfg{}
\set language sql
create table t(id int primary key, v text);
insert into t values (1, 'a') 
insert into t values (2, 'b') 
insert into t values (3, 'c') 
insert into t values (4, null)
insert into t values (5, null)
insert into t values (6, null)
select * from T order by v
---
- - [4, null]
  - [5, null]
  - [6, null]
  - [1, 'a']
  - [2, 'b']
  - [3, 'c']
... 

select * from T order by v desc
---
- - [3, 'c']
  - [2, 'b']
  - [1, 'a']
  - [4, null]
  - [5, null]
  - [6, null]