[css-ui] `interactivity` needs to apply to text

[Loirooriol]

https://drafts.csswg.org/css-ui/#inertness

Applies to: all elements
Inherited: yes

It applies to all elements. Therefore, it applies to inline elements.
Properties that apply to inline elements and are inherited also need to apply to text to as per #5303 (comment)

Indeed, this text in unselectable on Chromium canary:

<div style="interactivity: inert; display: contents">I'm inert</div>

Which, by the way, means that Blink also applies user-select to text.