Render LaTeX labels with the shape's font color, instead of stroke

[rachtsingh]

LaTeX labels were filled with the shape's stroke color, so they ignored style.font-color. This gives more flexibility to set font colors independent of the stroke (a feature I'm currently trying to use). I guess this ties it to font-color instead of stroke, but I think that's more reasonable (and you can always customize using LaTeX textcolor).

Applies to both SVG output (d2svg) and PNG/PDF/PPTX/GIF exports (d2scenebuild).

Example:

eq: |latex
  e^x
| {
  shape: rectangle
  style.stroke: black
  style.font-color: blue
}