Continues the work of #31318 and #31323 by correcting the behaviour of the alt text and changing the strings to match the work done in #31318

Background

To read why this change is very important see #31318

Testing Part 1

Testing is really easy. No npm, js or css involved.
Merge the pull request and then create a newsfeed (you can use https://community.joomla.org/blogs/community.feed and in the options add a first and second image

Testing Part 2

Please test three scenarios when you display the newsfeed from the menu

1. Image Description (Alt Text) = Empty
   No Description = unchecked

2. Image Description (Alt Text) = "some description"
   No Description = unchecked

3. Image Description (Alt Text) = Empty
   No Description = checked

The expected behaviour for each of these tests is

1.<img src="filename.jpg">
2. <img src="filename.jpg" alt="some description">
3. <img src="filename.jpg" alt >
or <img src="filename.jpg" alt="">

PLEASE do not comment on what you think the code does but apply the PR and test it. Getting very tired of people blocking PR with their comments without actually testing the code.

cc @carcam