debugui: remove Widget

Let's revisit when widget APIs are settled.

Author: hajimehoshi

example/ui.go

@@ -130,7 +130,7 @@ func (g *Game) testWindow(ctx *debugui.Context) {
 				ctx.Text("Blue:")
 				ctx.Slider(&g.bg[2], 0, 255, 1)
 			})
-			ctx.Widget(func(bounds image.Rectangle) debugui.EventHandler {
+			ctx.GridCell(func(bounds image.Rectangle) {
 				ctx.DrawWidget(func(screen *ebiten.Image) {
 					scale := ctx.Scale()
 					vector.DrawFilledRect(
@@ -149,7 +149,6 @@ func (g *Game) testWindow(ctx *debugui.Context) {
 					op.SecondaryAlign = text.AlignCenter
 					debugui.DrawText(screen, txt, op)
 				})
-				return nil
 			})
 		})
 		ctx.Header("Number", true, func() {

widget.go

@@ -88,16 +88,6 @@ func (c *Context) updateWidget(id WidgetID, bounds image.Rectangle, opt option)
 	return
 }
 
-func (c *Context) Widget(f func(bounds image.Rectangle) EventHandler) EventHandler {
-	pc := caller()
-	id := c.idFromCaller(pc)
-	return c.wrapEventHandlerAndError(func() (EventHandler, error) {
-		return c.widget(id, 0, func(bounds image.Rectangle, wasFocused bool) (EventHandler, error) {
-			return f(bounds), nil
-		})
-	})
-}
-
 func (c *Context) widget(id WidgetID, opt option, f func(bounds image.Rectangle, wasFocused bool) (EventHandler, error)) (EventHandler, error) {
 	c.currentID = id
 	r, err := c.layoutNext()