Update: use alt instead of aria-label for image alternative text (fixes #822)

[kirsty-hames]

Fixes #822

Update

• replace image aria-label with alt
• remove image aria-hidden

Testing confirmed all major screen readers handle alt and aria-label equivalently and Adapt would benefit from the broader benefits of alt. Benefits include:

• alternative text displayed when image fails to load
• alternative text retained when copying images into Word or similar tools.

Testing also confirmed an empty alt tag (alt="") is widely supported by screen readers / browsers to ignore an image without the need for aria-hidden.

Related

• Boxmenu header image - Update: remove header image aria-hidden (fixes #230) adapt-contrib-boxMenu#231
• Hotgraphic main image - Update: use alt instead of aria-label for image alternative text (fixes #356) adapt-contrib-hotgraphic#357
• LanguagePicker image - Update: remove header image aria-hidden (fixes #126) adapt-contrib-languagePicker#127
• Tutor feedback image - Update: use alt instead of aria-label for image alternative text (fixes #122) adapt-contrib-tutor#123

[cahirodoherty-learningpool]

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