Shared Array Buffer support

[stevefan1999-personal]

I see that there is no support for shared buffer which is important for wasmtime integration in Den, because the user can mutate the underlying WebAssembly memory object inside Javascript, but right now all the API in rquickjs requires creating copied value from Rust, rather than from a slice. I tried to sidestep it by doing this:

    #[qjs(get, enumerable)]
    pub fn buffer<'js>(&self, ctx: Ctx<'js>) -> Result<ArrayBuffer<'js>> {
        let data = self.inner.data(self.store.lock().unwrap().as_context());

        let val = unsafe {
            let val = qjs::JS_NewArrayBuffer(
                ctx.as_raw().as_mut(),
                data.as_mut_ptr(),
                data.len().try_into().unwrap(), 
                None, // No need for deallocation
                ptr::null_mut(), // No opaque
                1, // True = Shared
            );
            if qjs::JS_VALUE_GET_NORM_TAG(val) == qjs::JS_TAG_EXCEPTION {
                return Err(rquickjs::Error::Exception);
            }
            Value::from_js_value(ctx.clone(), val)
        };

        let buffer = ArrayBuffer::from_object(Object::from_value(val)?).unwrap();
        Ok(buffer)
    }

But function from_js_value is private and there seems to be no way to create that Rust-based value wrapper as well.