Enhanced keyboard navigation for Offcanvas.

[Owlbertz]

On open not the first element within the side panel, but the whole panel should receive focus.
If the first interactive element is focussed the user might miss some content above it, e.g. the panel heading.
Also added usage of handleKey() to the component to close the panel.
Moved the panel focussing outside of the transitionEnd listener because this was never called and it also works outside...

I would really appreciate feedback of @sethkane and @Geczy here.

[Geczy]

Took a look and that definitely makes the off canvas menus behave better under accessible software. But my issue still remains #8536

I work around it by adding $('#my-info').attr('aria-hidden', 'false'); on dom ready

[Owlbertz]

Huh, didn't saw that issue yet. Will try to get this done soon as well in the same branch.

[Owlbertz]

@Geczy Do you work with standard visibility classes? I feel like a simple this.$element.is(':visible') check before applying the aria-hidden (and also the aria-expanded stuff I guess) would do the trick during the initialization.

[rafibomb]

@Owlbertz That solution should work!

[mr-feek]

since this added keyboard as a dependency to off canvas, it would have been nice to have noted that in the documentation!