New Scoped css support doesn't render child combinators right

[sidjai]

Description of Issue

Tried to update to 5.7.1 from 5.6.x and all the css with child combinators didn't get attached in the render. Scoped css renders the data attribute on the child instead of first element which I think caused this.

Stack Trace / Console Log

input ( in file )
.top > child

expect ( in render ):
.top[data-thing] > child

Actual ( in render ):
.top > child[data-thing]

Additional Comments

Should follow this I think: https://vue-loader.vuejs.org/guide/scoped-css.html#deep-selectors