Add spread operator and multiple switch cases support

[princemaple]

Summary

• Add spread operator (...) support in arrays, objects, and function call arguments
• Support fallthrough pattern for multiple @case statements sharing a single block

Test plan

• Verify spread in arrays: {{ [a, ...rest, b] }}
• Verify spread in objects: {{ { a: 1, ...obj } }}
• Verify rest arguments: {{ func(a, ...args) }}
• Verify multiple case fallthrough:

  @case (1)
  @case (2)
  @case (3) {
    <span>Matched</span>
  }

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