fix: make last(empty) yield no output values

[itchyny]

This patch fixes last/1 to produce no output value when the argument yields nothing. For example, [last(empty)] and [last(range(0))] now produce [] instead of [null]. I fixed the issue using byte-coded definition, to avoid unnecessary value boxing. This closes #1869 and closes #3177.

[wader]

Maybe should say "last(g) where g does not output any value" so that it does not sound like it's a special case for exactly argument "empty"?

[itchyny]

I fixed the comment.

[wader]

Trying to understand what kind of "pesudo"-jq this translates, will

last(g)

be something like (vm is not limited by scoping rules?)

( true as $is_empty
| ( g as $last
  | false as $is_empty
  | empty
  )
// if $is_empty then empty else $last end
)

[itchyny]

Closer to write with reduce;

def last(g): reduce g as $item (
  { last: null, is_empty: true };
  .last = $item | .is_empty = false
) | if .is_empty then empty else .last end;

[itchyny]

Thank you.

[01mf02]

This is a very welcome change and brings jq and jaq closer together. Thank you!