Language: Spread operator (...) in arrays and calls

[PurHur]

Problem

[...$a, ...$b] and foo(...$args) are parsed but not compiled.

Goal

Unpack packed arrays into calls and array literals (VM first).

Tasks

• Compiler lowering for Unpack nodes
• VM: merge hashtables / arg list building
• JIT: defer or lower to runtime helper
• PHPT: array_merge equivalent via spread

Acceptance

$a = [1, 2];
$b = [3, ...$a];
// $b === [3, 1, 2]