feat(color): support better color interpolation for sequential schemes

[kristw]

🏆 Enhancements

• add modifyRange option to createLinearScale(domain, modifyRange = false). This extends the original behavior that always modify domain if needed.

   * Return a linear scale with a new domain interpolated from the input domain
   * to match the number of elements in the color scheme
   * because D3 continuous scale uses piecewise mapping between domain and range.
   * This is a common use-case when the domain is [min, max]
   * and the palette has more than two colors.
   *
   * @param domain domain of the scale
   * @param modifyRange Set this to true if you don't want to modify the domain and
   * want to interpolate range to have the same number of elements with domain instead.

• add extent option for .getColors(numColors, extent) to reduce the range of the color scheme, inspired SchemeParams option in vega-lite

   * Get colors from this scheme
   * @param numColors number of colors to return.
   * Will interpolate the current scheme to match the number of colors requested
   * @param extent The extent of the color range to use.
   * For example [0.2, 1] will rescale the color scheme
   * such that color values in the range [0, 0.2) are excluded from the scheme.

• Use HCL color space interpolation instead of RGB interpolation https://bl.ocks.org/mbostock/3014589
• Add more code comments for auto-complete
• Add more unit tests

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[codecov]

Codecov Report

Merging #547 into master will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #547      +/-   ##
==========================================
- Coverage   23.21%   23.12%   -0.09%     
==========================================
  Files         291      291              
  Lines        6790     6820      +30     
  Branches      675      684       +9     
==========================================
+ Hits         1576     1577       +1     
- Misses       5176     5204      +28     
- Partials       38       39       +1     

Impacted Files	Coverage Δ
packages/superset-ui-color/src/SequentialScheme.ts	100.00% <100.00%> (ø)
...ns/plugin-chart-word-cloud/src/chart/WordCloud.tsx	0.00% <0.00%> (ø)
...hart-word-cloud/src/legacyPlugin/transformProps.ts	59.09% <0.00%> (+9.09%)	⬆️

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[ktmud]

Can replace range with [...new Array(steps).keys()]

[kristw]

@ktmud d3.quantize and d3.piecewise are awesome.

[ktmud]

d3 API is full of gems like this. 😄 I didn't actually know d3.piecewise when I started reviewing this PR.