[css-selectors] Support universal selector usage with tagname *tagname

[brandonmcconnell]

Currently, all/most selectors support use after the universal selector.

For example…

w/ universal selector	w/o universal selector	identical targeting
*.class	.class	✅
*#id	#id	✅
*[attribute]	[attribute]	✅
*:pseudo	:pseudo	✅
*::pseudo	::pseudo	✅
*elem	elem	❌

Some advantages to allowing the universal selector to prepend tagname selectors are:

• better consistency in how all selectors behave with the universal selector

• easier nesting syntax agreed upon nesting syntax

  Up until now, the generally accepted and voted upon nesting syntax requires wrapping a selector with something like :is() or :where() when it begins with an alpha character since that could easily be confused with a CSS property name. That can look something like this:

  a:hover {
    color: hotpink;
    :is(aside) & {
      color: red;
    }
  }

  With this change to how the universal selector works next to tagnames, this same block could now be rewritten much more concisely using * like this:

  a:hover {
    color: hotpink;
    *aside & {
      color: red;
    }
  }

---

I put together a pen for this which can be used for demonstrating this proposal and also to test if/when this is implemented:
https://codepen.io/brandonmcconnell/pen/eYjYVrE

[Loirooriol]

Duplicate of #8253.