Control focus is lost on hide

[sunergeo]

I am using this control as a full-page cover to show activity during my ajax calls. However, once the call is completed, the focus is lost - it's set to document, rather than the last control that had the focus.

[ankurk91]

https://github.com/bootstrap-vue/bootstrap-vue/blob/45635d1d391263192787e9e0bddc004abe115ace/src/components/modal/modal.js#L752