Non-strict this coercion

Date: 2026-05-15 Area: engine Pull Request: #645

Completed the non-strict compatibility surface from #586 by making regular function calls coerce nullish this to globalThis behind --compat-non-strict-mode in interpreter and bytecode modes. Bytecode function templates now serialize their strict-this mode, the bytecode format is v30, the CLI/config tests cover the behavior, and the arguments-object helper lives in the value namespace as Goccia.Values.ArgumentsObjectValue. language.md. bytecode-vm.md. value-system.md.