Port ed50c2393a to glitch-soc

Port 89c6d2bd6b to glitch-soc

* Add aria-autocomplete='list' in Textaria

ref: https://www.w3.org/TR/wai-aria-1.1/#aria-autocomplete

* Make detect empty string brefore assign upload description

* Change code elements in keyboard-shortcuts component to kbd

* Add Keyboard Shortcuts Legend

Adds a "Keyboard Shortcuts" legend (displayed in the rightmost column)
which is toggled via a new "?" hotkey. When subsequently pressed from
the Keyboard Shortcuts legend, "?" will navigate back to the previous
location.

* Add hidden table headings.

Makes the headings available for accessibility but hides them visually.