Port arguments object optimizations

- Add pre-computed JSShape objects for arguments, mapped_arguments
- Use fast_array mode with var_refs for JS_CLASS_MAPPED_ARGUMENTS
- Arguments object elements now alias function parameters via JSVarRef
- Add js_mapped_arguments_finalizer and js_mapped_arguments_mark
- Modify JS_NewObjectFromShape to accept props parameter for initialization
- Add js_create_var_ref function for creating detached var_refs
- Add var_refs to GC immediately in get_var_ref (instead of at close time)

The mapped arguments optimization allows arguments[i] to directly reference
function parameters, enabling changes to propagate bidirectionally in
non-strict mode functions.

Ref: bellard/quickjs@9f11034

Author: saghul