[ES|QL] Allow nested non-correlated subqueries in from command

[fang-xing-esql]

#135744 enables non-correlated subquery in from command, this is a follow up issue to enable nested non-correlated subqueries in the from command.

FROM index1,
     (FROM index2,
           (FROM index3,
                  (FROM index4 
                   | WHERE a > 0)  
            | STATS count(*)) 
      | STATS count(*))
| WHERE h > 10
| EVAL i = h * 2
| STATS cnt = COUNT(*) BY j
| SORT cnt desc
| DROP k
| KEEP l
| LIMIT 1000

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)