ESQL: Optimize more CASE cases

[nik9000]

ESQL's case is lazy and so quite slow. We run it eagerly in a few cases, but not enough. I've encountered a query like:

FROM foo
| EVAL action = CASE(
    a IN ("a", "b", "c"), "a",
    a == "d", "d"
)
| WHERE action == "d"

Where we do not optimize the CASE statement here. There are two "obvious" optimizations for this:

1. Run CASE in non-lazy mode - maybe even a switch style mode.
2. Push the filter a == "d" into the index transitively.

[elasticsearchmachine]

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