Fix a DST error in date_histogram (backport of #52016)

[nik9000]

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 Longs 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 Strings which are
then parsed back to Instants which are then convertd to longs. 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 #50265