This prevents `CONCAT` from using an unbounded amount of memory by
hooking it's temporary value into the circuit breaker. To do so, it
makes *all* `ExpressionEvaluator`s `Releasable`. Most of the changes in
this PR just plumb that through to every evaluator. The rest of the
changes correctly release evaluators after their use.
I considered another tactic but didn't like it as much, even though the
number of changes would be smaller - I could have created a fresh,
`Releasable` temporary value for every `Page`. It would be pretty
contained keep the releasable there. But I wanted to share the temporary
state across runs to avoid a bunch of allocations.
Here's a script that used to crash before this PR but is fine after:
```
curl -uelastic:password -XDELETE localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test -d'{
"mappings": {
"properties": {
"short": {
"type": "keyword"
}
}
}
}'
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test/_doc/1?refresh -d'{"short": "short"}'
echo -n '{"query": "FROM test ' > /tmp/evil
for i in {0..9}; do
echo -n '| EVAL short = CONCAT(short' >> /tmp/evil
for j in {1..9}; do
echo -n ', short' >> /tmp/evil
done
echo -n ')' >> /tmp/evil
done
echo '| EVAL len = LENGTH(short) | KEEP len"}'>> /tmp/evil
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/_query?pretty --data-binary @/tmp/evil
```
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