Finish implementing Line and remove LineView

[tig]

This is a sub-issue of:

• Finish Adornments (master Issue)  #2994

Todo

• Implement Line class.
  • Enable line-ends like LineView has, so Line can replace it.
  • Enable mouse/keyboard movement of a Line (if CanFocus == true).
• Build a Line Demo scenario.
• Use Line within Border to support Add mouse/keyboard resizing of views #2537
• Nuke LineView
• Nuke LineViewExample scenario
• Nuke TileView ; use a tiled-layout mode instead. See Get rid of Toplevel - Introduce Runnable and Overlapped instead #2491.

Background

Sometime back I implemented Line. It is extremely simple right now:

/// <summary>
/// Draws a single line using the <see cref="LineStyle"/> specified by <see cref="View.BorderStyle"/>.
/// </summary>
public class Line : View {
	private Orientation _orientation;

	/// <summary>
	/// The direction of the line.  If you change this you will need to manually update the Width/Height
	/// of the control to cover a relevant area based on the new direction.
	/// </summary>
	public Orientation Orientation { get => _orientation; set => _orientation = value; }

	/// <summary>
	/// Constructs a Line object.
	/// </summary>
	public Line ()
	{

	}

	/// <inheritdoc/>
	public override bool OnDrawFrames ()
	{
		var screenBounds = BoundsToScreen (Bounds);
		LineCanvas lc;

		lc = SuperView?.LineCanvas;
		lc.AddLine (screenBounds.Location, Orientation == Orientation.Horizontal ? Frame.Width : Frame.Height, Orientation, BorderStyle);

		return true;
	}

	//public override void OnDrawContentComplete (Rect contentArea)
	//{
	//	var screenBounds = ViewToScreen (Frame);

	//}

	/// <inheritdoc/>
	public override void OnDrawContent (Rect contentArea)
	{
		OnDrawFrames ();
	}
}

Note the comments in the code are wrong and it's buggy (assumes Bounds == Frame).

My dream is that it gets enhanced to take the code that's in TileView for dragging an edge with keyboard/mouse (showing a diamond) so that I can be used as the basis for any "view edge drag operation".

If we do this, and then use Line objects for the top, right, bottom, and left of a view's Border frame, all mouse/keyboard dragging logic for View resizing (see #2537) will be nicely encapsulated.

TileView then can be removed and replaced with a tiled-layout mode. See #2491.