IPath: Remove unused features to enable simplifying and optimizing InternalPath

[antonfirsov]

After merging #96, InternalPath will become unnecessarily heavy both code and memory-wise.

Ideally it should only contain a PointF[] to be fed to TessellatedMultipolygon, the following stuff seems to be heavy and unnecessary:

ImageSharp.Drawing/src/ImageSharp.Drawing/Shapes/InternalPath.cs

Lines 933 to 965 in acf438b

	private struct PointData
	{
	public PointF Point;
	public Orientation Orientation;
	public float Length;
	public float TotalLength;
	public Segment Segment;
	}
	private struct PassPointData
	{
	public bool RemoveLastIntersectionAndSkip;
	public Orientation RelativeOrientation;
	public bool DoIntersect;
	}
	private readonly struct Segment
	{
	public readonly PointF Start;
	public readonly PointF End;
	public readonly PointF Min;
	public readonly PointF Max;
	public Segment(PointF start, PointF end)
	{
	this.Start = start;
	this.End = end;
	this.Min = Vector2.Min(start, end);
	this.Max = Vector2.Max(start, end);
	}
	}

The following features seem to rely on this data, I suggest to remove them from the public API, since they do not really serve drawing concerns:

• IPath.FindIntersections, IPath.MaxIntersections
• IPath.Distance
• IPath.PointAlongPath
• IPath.Length

Some of the above could be replaced with slow variants if we really want/need them.