ES|QL: leaking all-fields-projected attribute

[luigidellaquila]

On the sample dataset

from alerts

   host.name   |kibana.alert.risk_score
---------------+-----------------------
test-host-1    |21.0                   
test-host-2    |17.0                   

but if we override all the attributes

from alerts | eval  host.name = 1, kibana.alert.risk_score = 2

<all-fields-projected>|   host.name   |kibana.alert.risk_score
----------------------+---------------+-----------------------
null                  |1              |2                      
null                  |1              |2            
...         

[elasticsearchmachine]

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

[astefan]

Relates #120272

[astefan]

FROM languages | EVAL language_code = 3 | LOOKUP JOIN languages_lookup ON language_code

results in

<all-fields-projected>| language_code | language_name 
----------------------+---------------+---------------
null                  |3              |Spanish        
null                  |3              |Spanish        
null                  |3              |Spanish        
null                  |3              |Spanish