Opt-in loose equality

Date: 2026-05-11 Area: engine

Added opt-in loose equality compatibility (--compat-loose-equality / "compat-loose-equality"). == and != remain warning-producing no-ops by default, but when enabled they use the shared ES2026 IsLooselyEqual implementation in interpreter and bytecode modes, including string/number/boolean coercion, BigInt mixed comparisons, and object ToPrimitive; the bytecode format is bumped to v27 for OP_LOOSE_EQ and OP_LOOSE_NEQ. language.md.