Fixes esql class cast bug in STATS at runtime level

[ncordon]

Addresses the runtime side of #133992 and #136598. Builds on top of #137511

Queries like:

from airports 
rename scalerank AS x 
stats  a = count(x), b = count(x) + count(x), c = count_distinct(x)

They should never fail at runtime even if the plan was not optimal for repeated aggregations.

Closes #138653

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

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

[alex-spies]

Good change that's currently blocked on #138805.

There's a possible workaround but I"m not sure it's worth it.