Feature: expand crosshair on edges

[dan12411]

Description

When we like to join two chart with crosshair move together, the join side padding must be zero, otherwise crosshair will be cut like image below:

ps. By adding 50 px bottom padding on top chart.

Solution

By adding List<bool> expandEdges, we can decide crosshair expand on left, top, right and bottom directions respectively. Default value is [false, false, false, false]. And only work on RectCoord. - de0a30b

if we add line like this in top chart, we get no-cut crosshair:

  crosshair: CrosshairGuide(
     ...
     expandEdges: [false, false, false, true],
  ),

Additional fix for show LabelBackgroundMapper - 1857d18