[Feature] continuous visualMap to support different color space and custom stop values

[PaulBrnrther]

What problem does this feature solve?

Currently the continuous visual map allows only interpolation in an RGBA-Space.
For enabling the advantages of different color spaces (in particular of the CIELab color space which is better suited to create human-perceptually uniform gradients) it would be best to be able to choose the color space in which the interpolation between two colors is performed.

Currently the continuous visual map allows only equidistant interpolation by using multiple colors in the inRange property.
But it would be nice to be able to set such interpolation stop values manually.

What does the proposed API look like?

{ visualMap: { type: "continuous", colorSpace: "lab" | "rgba" | ..., inRange: { stopValues: number[], colors: string[] } }

[helgasoft]

all CSS color spaces are currently supported, lab included; see #20757.
But they do not work as stops in visualMap like inRange:{ color:["lab(50% 75 25)", "lab(50% 25 75)"].
However one could set the gradient this way:

    inRange: { 
      color: 'green',
      colorLightness: [0.8, 0.2], 
      colorSaturation: [0.5, 1],
      colorHue: 99
     },

[PaulBrnrther]

I gather that this will allow setting the stop values using my favorite color space but this is actually not my main concern (I can use an external library to translate my colors to rgb). My main concern is that the interpolation that happens between the given stop values is not configurable and it is different depending on the color space.
For example here there are only two stop values at the two ends of the gradient but the interpolations are in different spaces: