fix: Convert CSS color specifiers to rgba in gl traces

[camdecoster]

Description

Convert CSS color specifiers to rgba before passing them to regl libraries to avoid issues with syntax compatibility.

Closes #8116.

Changes

• Convert color specifiers
• Add tests

Screenshots

Before	After

Testing

• Be on main
• Open Plotly devtools and paste the following into the browser devtools console:

  const c = 'oklch(0.7 0.15 30)';
  const trace = {
      x: [1, 2, 3], y: [1, 3, 2], mode: 'lines+text', text: ['a', 'b', 'c'], textposition: 'top center',
      line: { color: c, width: 4 }, fill: 'tozeroy', fillcolor: c, textfont: { color: c, size: 20 },
      error_y: { array: [0.5, 0.5, 0.5], color: c, thickness: 3 }
  };
  Plotly.newPlot(gd, [
      { ...trace, type: 'scatter', name: 'scatter' },
      { ...trace, type: 'scattergl', name: 'scattergl', xaxis: 'x2', yaxis: 'y2' }
  ], { grid: { rows: 1, columns: 2, pattern: 'independent' }, width: 800, height: 400 });

• Note that the scattergl trace has the incorrect color
• Switch to this branch
• Run the snippet again
• Note that the scattergl trace has the correct color

Notes

• The underlying regl libraries that these traces use rely on an older color parsing library that doesn't parse modern CSS color specifiers (color-normalize v1.5.2)
• plotly.js already has the feature to convert modern specifiers to rgba, so I did that here