[Feature] Add inactiveColor, inactiveBorderColor, and inactiveBorderWidth to visualMap

[gioneves]

What problem does this feature solve?

Currently, visualMap does not provide built-in options to customize the appearance of inactive (unselected) elements in either piecewise or continuous modes. This limitation reduces visual clarity when certain values are deselected, making it difficult to distinguish active and inactive states effectively.

In contrast, the legend component already supports customization of inactive elements using inactiveColor, inactiveBorderColor, and inactiveBorderWidth. However, visualMap lacks these options, leading to inconsistencies when both components are used in the same chart.

For example, when using visualMap.piecewise, unselected categories always appear in a default style that cannot be modified. Similarly, in visualMap.continuous, there is no way to adjust the appearance of unselected ranges, making it harder to visually communicate inactive states.

Adding inactiveColor, inactiveBorderColor, and inactiveBorderWidth would allow users to fully control the appearance of inactive elements in both modes, improving chart customization and usability.

What does the proposed API look like?

The proposed API would introduce three new properties under visualMap that apply to both piecewise and continuous modes:

visualMap: {
  type: "piecewise",  // or "continuous"
  dimension: 2,
  pieces: [ // For piecewise mode
    { min: 0, max: 30, color: "blue" },
    { min: 31, max: 60, color: "orange" },
    { min: 61, max: 100, color: "green" }
  ],
  range: [20, 80], // For continuous mode
  inactiveColor: "#ccc",        // Customize the color of inactive elements
  inactiveBorderColor: "#ccc",  // Customize the border color of inactive elements
  inactiveBorderWidth: "auto"   // Allow automatic or manual control of inactive border width
}

This enhancement would ensure visual consistency between visualMap and the legend, allowing for better differentiation of inactive states in both piecewise and continuous visualizations.