When `date_histogram` attempts to optimize itself it for a particular
time zone it checks to see if the entire shard is within the same
"transition". Most time zone transition once every size months or
thereabouts so the optimization can usually kicks in.

*But* it crashes when you attempt feed it a time zone who's last DST
transition was before epoch. The reason for this is a little twisted:
before this patch it'd find the next and previous transitions in
milliseconds since epoch. Then it'd cast them to `Long`s and pass them
into the `DateFieldType` to check if the shard's contents were within
the range. The trouble is they are then converted to `String`s which are
*then* parsed back to `Instant`s which are then convertd to `long`s. And
the parser doesn't like most negative numbers. And everything before
epoch is negative.

This change removes the
`long` -> `Long` -> `String` -> `Instant` -> `long` chain in favor of
passing the `long` -> `Instant` -> `long` which avoids the fairly complex
parsing code and handles a bunch of interesting edge cases around
epoch. And other edge cases around `date_nanos`.

Closes elastic#50265