Opt-in while loops

Date: 2026-05-17 Area: engine Pull Request: #651

Added opt-in while and do...while JavaScript compatibility behind --compat-while-loops / "compat-while-loops" in interpreter and bytecode modes. The flag is separate from --compat-traditional-for-loop, stays off by default with the existing parser warning/no-op behavior, and supports condition testing, break, continue, return, timeout checks, instruction limits, and module/config propagation when enabled. language.md.