Consider new guidance to accommodate assistive technology support for some style markup

[mbgower]

As per #4109 and some explorations in:

1. b80a03d
2. ba248f9
3. 5853193

there may be room for new techniques or rephrasing of F2 to encompass supporting 1.3.1 by using presentation markup that is supported by assistive technologies as a means of achieving "programmatically determined". Given the definition of that term, there does not seem to be anything in the SC language preventing using, say, supported CSS attributes to communicate presentation meaning to ATs:

determined by software from author-supplied data provided in a way that different user agents, including assistive technologies, can extract and present this information to users in different modalities

Determined in a markup language from elements and attributes that are accessed directly by commonly available assistive technology.

Determined from technology-specific data structures in a non-markup language and exposed to assistive technology via an accessibility API that is supported by commonly available assistive technology.