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* Rename Bootstrap mixin to ``Bootstrap4TapeformMixin``, an alias is kept for
backward compatibility but it will be deprecated and removed at some time
* Remove 'small' CSS class from the help text in Boostrap mixin
* Use 'form-field-' as prefix for container CSS class instead of the value
returned by ``get_field_container_css_class``
* Add a new ``Bootstrap5TapeformMixin`` mixin for Bootstrap v5
* Add 'form-group' CSS class to checkbox container in Bootstrap mixin