Camelized Named arguments naming issue

`<@ItemComponent />` renders "OK", `{{@ItemComponent}}` -> throw error `Assertion Failed: '@ItemComponent' is reserved.`
reproduction: [Ember Twiddle](https://ember-twiddle.com/b4f0d498611309dbcb26c9577b768f17?openFiles=templates.components.my-books.books-list.hbs%2C)

Refs: https://emberjs.github.io/rfcs/0276-named-args.html#reserved-names

It's really confusing if you missed this paragrath in RFC, should we update error message to point to RFC link or offer differen name? Instead of Assertion Failed: '@ItemComponent' is reserved. show something like this: Assertion Failed: '@ItemComponent' is reserved. RFC 276#reserved-names try change {componentName} attribute name from "ItemComponent" to "itemComponent".