[Line Mark] Todos

[luucvanderzee]

Still missing from the current Line mark:

• Transitions when the Line is not represented as Polygon, so between LineStrings/MultiLineStrings. This has to be implemented in transshape first.
• A func prop, like the one we had in vue-gg, so that you can use the Line to plot functions
• Some extra styling options like stroke-linecap, stroke-linejoin and stroke-dasharray, which work natively for SVG, but would need custom implementations for canvas/webgl/polygon representations of the Line
• Improve the current line-join. It now looks identical to native svg lines, except for extremely small angles. In theory, you can make the join infinitely long by having a really small angle (don't worry if this doesn't make sense, I know what the problem is lol)