add support to `onFocusOnly` option for interactions

[rslemos]

Add support to onFocusOnly option that is available on ol/interaction/MouseWheelZoom and on ol/interaction/DragPan (and ol/interaction.defaults for completeness).

For the site I'm developing right now this is a must, since we have lots of scrollable content on a page with a map. Without onFocusOnly the map traps the mouse wheel, resulting in a bad user experience.

Please note that the tabindex thing in <aol-map> is needed for the focusWithTabindex condition to work inside OpenLayers. I don't expect any breaking change in this PR, given that in using [attr.tabindex] with null will effectively not set tabindex (as it occurs before the PR). Also, tabindex property didn't exist in aol-map altogether (so nobody should be using it).