Adding a "screen reader text" block option via themes

[justintadlock]

Discussed in #181

^{Originally posted by justintadlock December 13, 2023}
Currently, the best way to mark a Heading, Paragraph, or other block to only be shown to screen readers is to add the .screen-reader-text class via the Advanced tab.

What if there was a more user-friendly way? Maybe a simple toggle switch in the block settings?

Building off the Beyond Block Styles tutorial series, I'd like to explore how we can add something a little simpler that could have a potentially big impact for folks who need the ability to mark text for screen readers only.