When `jQuery.noConflict` is called, the global `$` variable is not
defined. We cannot assume in the code that the variable is defined,
and instead should always make sure to import the `jquery` module
when we need jQuery.
This fixes all of the issues where we are assuming that `$` is
defined globally when we are not importing the module. This also
fixes the issues when defining the `jQuery.fn.select2.amd` modules
where we were always attaching to the `$` object instead of the
`jQuery` object.
This closes https://github.com/select2/select2/issues/2947.
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.
