Code Insights: add hover state to active data series and key items

Created by: AlicjaSuska

Description Connected to #35771

As per design - when user hovers on an active data series or on key item the line should be highlighted and brought to the top (changed z-index), other lines should be faded out.

@coury-clark's loom shows the correct behaviour (time: 1:55)

Slack thread for more context.