Allow wrapping Ruby and JS object to each other

[kateinoigakukun]

This PR adds Ruby's JS::Object <-> JS's RbValue object interoperability by wrapping them with each other.

Example

// JS -> Ruby object
const hash = vm.eval(`Hash.new`)
hash.call("store", vm.eval(`"key1"`), vm.wrap(new Object()));

# Ruby -> JS object
js_obj = JS.eval(`return {}`)
js_reflect = JS.eval("return Reflect")
js_reflect.call(:set, JS::Object.wrap(Object.new))