Full width image carousel

# Feature Request

## Is your feature request related to a problem? Please describe

One of the most common uses of the Carousel-CE is a picture carousel across the full width of the screen. At the moment, as far as I know, this is only possible by setting the images as background_image and the carousel to "no border". But this has three main disadvantages:

- background images are not indexed by Google.
- background images do not have an alt-tag, which could be used for SEO purposes
- the background images are automatically cropped to the size of the carousel. It is hardly possible for the editor to control where or how the image is cropped.

## Describe the solution you'd like

It should be possible to set images in the Carousel with a 100% width (instead of a fixed pixel width). The aspect ratio of the image should be maintained so that you have control over a possibly necessary crop in the image editor.
For example, the bootstrap carousel does it, with the class="d-block w-100".

Start by locating the Carousel-CE implementation and its current image rendering, then compare its behavior with the Bootstrap carousel example using d-block w-100. The change is complete when carousel images can use 100% width, preserve their aspect ratio, and retain usable alt text without relying on background images.

Written by the indexing model from the issue text.