Harmonise hover interaction across chart types (where sensible)

[sophiamersmann]

Closely related to #3918 and #3381

• On hover, some chart types increase the opacity of the hovered element, while others brighten the element's colour (Marimekko) or de-emphasize non-hovered elements in different ways (either by reducing the opacity or by using grey)
• Thinking about selection states or thinking about the opacity of chart elements also forces us to think about hover interactions. These issues should probably be solved in tandem