Previously Select2 would assume that the tab index for the
`<select>` was `0`, which is the browser default. Now Select2 will
clone the tab index from the original element, and correctly restore
it when it is destroyed or disabled/enabled.
This closes https://github.com/select2/select2/issues/3031.
This adds basic tests to ensure that the selection is accessible by
all users. This checks for common attributes, ensuring that the
container is always keyboard accessible and follows ARIA guidelines.
This also changes the base selection to create a common element so
we don't need to repeat attributes and such across multiple selection
containers.