Bug 37988: Use Bootstrap 5 class .visually-hidden-focusable

Bug 37988: Use Bootstrap 5 class .visually-hidden-focusable

It looks to me like we can remove the visibility properties from the
home button CSS and wrap the text in a <span> with Bootstrap 5's
"visually-hidden-focusable" class:

https://getbootstrap.com/docs/5.3/getting-started/accessibility/#visually-hidden-content

That appears to give us the behavior we want: A focusable icon which
isn't obscured by the focus border.

To test, apply the patch and rebuild the staff interface CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_interface).

In the staff interface, test some pages by using tab or shift-tab to
move between elements on the page to confirm that the home icon can be
tabbed to.

Signed-off-by: Olivier Vezina <olivier.vezina@inLibro.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>