When CASE hits a multivalued field it was previously either crashing on
fold or evaluating it to the first value. Since booleans are loaded in
sorted order from lucene that *usually* means `false`. This changes the
behavior to line up with the rest of ESQL - now multivalued fields are
treated as `false` with a warning.
You might say "hey wait! multivalued fields usually become `null`, not
`false`!". Yes, dear reader, you are right. Very right. But! `CASE`'s
contract is to immediatly convert its values into `true` or `false`
using the standard boolean tri-valued logic. So `null` just become
`false` immediately. This is how PostgreSQL, MySQL, and SQLite behave:
```
> SELECT CASE WHEN null THEN 1 ELSE 2 END;
2
```
They turn that `null` into a false. And we're right there with them.
Except, of course, that we're turning `[false, false]` and the like into
`null` first. See!? It's consitent. Consistently confusing, but sane at
least.
The warning message just says "treating multivalued field as false"
rather than explaining all of that.
This also fixes up a few of CASE's docs which I noticed were kind of
busted while working on CASE. I think the docs generation is having a
lot of trouble with CASE so I've manually hacked the right thing into
place, but we should figure out a better solution eventually.
Closes#112359
This updates the in-code docs on the trig functions to line up with the
docs, removes the docs, and uses the now mostly identical generated
docs. This means we only need to document these functions in one place -
right next to the code.
This modifies the ESQL test infrastructure to generate more of the
documentation for functions. It generates the *Description* section, the
*Examples* section, and the *Parameters* section as separate files so we
can use them as needed. It also generates a `layout` file that's just
a guess as to how to render the whole thing. In some cases it'll work
and we can use that instead of hand maintaining a "top level"
description file for the function.
Most newly generated files are unused. We have to chose to pick them up
by replacing the sections we were manually maintaining with an include
of the generated section. Or by replacing the entire hand maintained
file with the generated top level file.
Relates to #104247
