feat: combine arcs #1748

[jguddas]

It works, but there are still a couple of to-dos I currently don't have the time to fix.

svgo/plugins/convertPathData.js

Lines 416 to 445 in 8852d3f

	for (
	j = index;
	// @ts-ignore
	path[j++] &&
	// @ts-ignore
	(nextArc = findArc(arc.item.coords, path[j - 1], {
	error,
	arcThreshold,
	arcTolerance,
	})) &&
	nextArc;
	) {
	// TODO: if (nextArc is full circle) break;
	// TODO: if (nextArc center is outside of tolerance) break;
	// @ts-ignore
	arc.item.coords = nextArc.item.coords;
	// @ts-ignore
	arc.item.args[5] = arc.item.coords[0] - arc.item.base[0];
	// @ts-ignore
	arc.item.args[6] = arc.item.coords[1] - arc.item.base[1];
	}
	// TODO check that stringify is shorter
	command = 'a';
	data = arc.item.args;
	// @ts-ignore
	item.coords = arc.item.coords;
	// filter out consumed next items
	path.splice(index + 1, j);

This provides the foundation for #1748.

[jguddas]

This currently creates useless 0 width path segments.