3936 add alt text to social media buttons

[StephDriver]

• Share icons now have aria-labels on OLH and Material themes (no share icons found on Clean).
• Dyslexia, text size, print icons now have aria-labels on OLH (not found on Material or Clean).
• How to Cite icon now has Aria label and is no longer invisible to screen reader or keyboard navigation (tested with Mac Voice-over). The dropdown inside it for different citation format also now works with tab and screen reader.
• The options hamburger button for narrow windows how has an aria label for 'options'.

All tested with Mac Voice Over. Related bugs noticed (such as difference in order between visual and tab) which will feed into the current A11y audit, but as for what was reported in this issue, that has now been fixed.

Closes #3936

[ajrbyers]

This is great but as they're on the front of house we should mark the aria-labels as translatable!