Add context response to Infrared Absorbance slider when there are no layers in the atmosphere

[arouinfar]

The Infrared Absorbance of the layers can be adjusted even when no layers are in the atmosphere. This supports prediction-making and generally makes it easier to set up experiments. However, it can be a bit confusing to screen reader users.

When there are layers in the atmosphere, there is a context response that states: All layers now absorbing {{70%}} of infrared photons{{, {{30%}} passing through layers}}.

However, nothing is stated if there are no layers currently in the atmosphere. Based on interview feedback, we would like to add this context response:

No absorbing layers. Added layers will absorb {{80%}} of infrared photons.

[jbphet]

This has been added. Below is a screenshot from the a11y view when playing with it. Keep in mind that this, like the other IR absorbance alerts, requires the sun to be shining.

Assigning to @arouinfar for review.

[arouinfar]

Looks good on main, thanks @jbphet. Closing.