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

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

Fixes #3997.

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