widget/material: add disabled state support to all widgets

This commit configures all remaining widgets to draw themselves in a disabled state
when their layout.Context is disabled. A description of the
strategy employed by each follows:

- Checkbox and RadioButton: Draws the icon component in a lighter color. Currently the label text is left
in its default color.
- ProgressBar: The "progress" color is lightened, but not as much as the background color. This makes the current progress value still readable.
- Editor: The cursor is no longer drawn and the text is lightened.
- Switch: The track is unchanged, but the circular "thumb" component is lightened.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/material/editor.go

@@ -52,13 +52,20 @@ func (e EditorStyle) Layout(gtx layout.Context) layout.Dimensions {
 		gtx.Constraints.Min.Y = h
 	}
 	dims = e.Editor.Layout(gtx, e.shaper, e.Font, e.TextSize)
+	disabled := gtx.Queue == nil
 	if e.Editor.Len() > 0 {
-		paint.ColorOp{Color: e.Color}.Add(gtx.Ops)
+		textColor := e.Color
+		if disabled {
+			textColor = mulAlpha(textColor, 150)
+		}
+		paint.ColorOp{Color: textColor}.Add(gtx.Ops)
 		e.Editor.PaintText(gtx)
 	} else {
 		call.Add(gtx.Ops)
 	}
-	paint.ColorOp{Color: e.Color}.Add(gtx.Ops)
-	e.Editor.PaintCaret(gtx)
+	if !disabled {
+		paint.ColorOp{Color: e.Color}.Add(gtx.Ops)
+		e.Editor.PaintCaret(gtx)
+	}
 	return dims
 }