Update old after/before pseudo-element reference link in section 4.3.2 F

[rahimabdi]

This feedback is for Name and Description Computation 1.2 Editor's Draft: https://w3c.github.io/accname/.

In section 4.3.2 F, the ::before and ::after reference is out of date: https://www.w3.org/TR/CSS2/generate.html#before-after-content.

I believe this is the latest CSS Selectors Level 3 reference for ::after/::before: https://www.w3.org/TR/selectors-3/#gen-content.

[rahimabdi]

Upon further investigation, the CSS2 reference to ::before and ::after (https://www.w3.org/TR/CSS2/generate.html#before-after-content) has much more detail about the behavior of these pseudo-elements. The CSS3 reference (https://www.w3.org/TR/selectors-3/#gen-content) is more concise and references the CSS2 spec.

I'd love to get others' thoughts on which CSS spec link we should use for generated content.

I also found another instance of a CSS2 reference that may need to be modified if we choose to update to CSS3 links: A.1 Normative References (https://w3c.github.io/accname/#normative-references).