[context menu] Add visual clues

[markov00]

With the new context menu (right-click on the chart), there are a set of visual clues that can be considered to improve the experience.
In particular:

• a visual clue could be used to describe that the tooltip is pinned (an icon, a different shadow, a border). This could help understand why a tooltip is not moving anymore, in particular when you have pinned a tooltip with no action (aka tooltip with more than X values).
• add an indicator to the pinned geometry in flame graph (check also the need on other charts)
  
• understand if we need to differentiate the style of a "bucket list of items" tooltip vs a "only hovered items" tooltip
• delay/animate the change of tooltip content, in particular when its content change from a bucket list to a highlighted one