Move Non-props attributes to the separate section in docs

[NataliaTepluhina]

Currently, $attrs are explaine within Component props section and I believe it's not that obvious and makes it harder to find guide on attributes fallthrough. I propose to move it to the separate page (maybe also extend it with some examples)

[bencodezen]

We also need to update this section with what's going on in this RFC:

https://github.com/vuejs/rfcs/blob/master/active-rfcs/0031-attr-fallthrough.md

I encountered some gotchas in documenting something else where we need to explain how listeners are now a part of attrs.

Let me know if you need help or have questions!