Turn "Rename image" feature into a proper "Add alt text"

[druxstr]

The image toolbar doesn't provide any explicit way to add an alt text to an image. This is an accessibility issue.

This said, there is a non-explicit way to add an alt : you use the "Rename image" feature.

When renaming the image, the input text is used as a alt attribute for the <img>

Proposal : rename the "Rename image" into "Add a text alternative for the image".

It will provide an explicit accessibility feature, while hurting almost no one.