fix(popover): enable pointer events only for popover content
fix(popover): enable pointer events only for popover content

The popover window element or its arrow may cause extra `mouseleave` and
`mouseenter` events when moving the mouse slowly from the direction of the
appearing popover, preventing it from appearing.

jnizet/ng-bootstrap,ng-bootstrap/ng-bootstrap,jnizet/ng-bootstrap,fbasso/ng-bootstrap,fbasso/ng-bootstrap,fbasso/ng-bootstrap,ng-bootstrap/ng-bootstrap,fbasso/ng-bootstrap,ng-bootstrap/ng-bootstrap,ng-bootstrap/ng-bootstrap,jnizet/ng-bootstrap,jnizet/ng-bootstrap