Final call: Rename "form control" to "form field" #1411

Hey folks,
Another final call, this time to clarify the name of the "form control has
non-empty accessible name" rule. This change renames the phrase "form
control" to "form field", to more clearly distinguish input / select
elements from buttons.

This final call ends on August 20th. If you have any feedback, please leave
a review before that time:
https://github.com/act-rules/act-rules.github.io/pull/1411

-- 
*Wilco Fiers*
Axe for Web product owner - Co-facilitator WCAG-ACT - Chair ACT-R