Add Hide teaser help text in More block.

[gziolo]

Description

Replaces #6561 which was started by @samikeijonen.

Adds Hide teaser help text in More block as mentioned in #2146.

This implementation is based on feedback shared by @afercia in #8974 (comment):

The help text has been changed in #11587, but still not so clear:

More
Mark the excerpt of this content.
Content before this block will be
shown in the excerpt on your
archives page.


Hide the teaser before the "More" tag

I'd like to suggest to change it into:

More
Content before this block will be
shown in the excerpt on your
archive pages.


Hide the excerpt on the full content page

#6561 (comment):

I'd like to propose something along the lines of the screenshot below:

As discussed at length during the implementation of the switch toggle, for better accessibility:

• an UI control accessible name (the label) should not change dynamically
• the state should indicated separately: a textual representation of the state is the only guarantee this information can be perceived by everyone

Screenshots

[jorgefilipecosta]

Code wise looks good to me and worked well in my tests 👍

[samikeijonen]

Thanks for this!