Remove will-change CSS rule for Overlay container
Remove will-change CSS rule for Overlay container

Fixes #9467
Fixes #9139

Chrome doesn't force a composition if the `will-change` CSS rule is different from `transform` or `opacity`.
See https://bugs.chromium.org/p/chromium/issues/detail?id=960953

openlayers/openlayers,geekdenz/openlayers,bjornharrtell/ol3,geekdenz/ol3,tschaub/ol3,geekdenz/ol3,oterral/ol3,tschaub/ol3,openlayers/openlayers,stweil/openlayers,adube/ol3,adube/ol3,geekdenz/ol3,bjornharrtell/ol3,stweil/openlayers,oterral/ol3,ahocevar/ol3,tschaub/ol3,oterral/ol3,ahocevar/openlayers,adube/ol3,stweil/ol3,geekdenz/ol3,stweil/ol3,ahocevar/openlayers,ahocevar/ol3,ahocevar/ol3,bjornharrtell/ol3,ahocevar/ol3,stweil/openlayers,ahocevar/openlayers,geekdenz/openlayers,stweil/ol3,tschaub/ol3,openlayers/openlayers,stweil/ol3,geekdenz/openlayers