Refactor: share iconAction for borderless 16 DIP icon buttons

datetimeIconButton moves to icon_button.go as iconAction(c, icon, label)
and replaces the identical copies in Dialog close, PasswordInput toggle
and AppShell collapse. Hover and press now set Text on every caller,
including the date and time pickers, which kept TextMuted on hover.
Image retry (bordered, danger ink), TagsInput remove (14 DIP icon, no
press state) and Tag close (12 DIP icon, fade) are different buttons
and stay as they are.

datetime.go

@@ -122,21 +122,6 @@ func datetimeDayLabel(c *ui.Context, d Date) string {
 	return fmt.Sprintf(msg(c, "calendar.day_label"), wd, datetimeMonthName(c, d.Month), d.Day, d.Year)
 }
 
-// datetimeIconButton is a square, borderless button showing icon, named label.
-func datetimeIconButton(c *ui.Context, icon, label string) *ui.Element {
-	k := Tokens(c)
-	b := ui.ButtonBase(c).Size(theme.MinHitSize, theme.MinHitSize).Radius(theme.ControlRadius).Label(label)
-	internal.Ring(b, k.Focus, theme.ControlRadius)
-	switch {
-	case b.Pressed():
-		b.Background(k.Selection)
-	case b.Hovered():
-		b.Background(k.SurfaceHover)
-	}
-	b.TextColor(k.TextMuted).Children(func() { ui.Icon(c, icons.Must(icon)).Size(16, 16) })
-	return b
-}
-
 // datetimeField styles row as a single-line field: solid fill and fine border.
 func datetimeField(c *ui.Context, row *ui.Element, invalid, readOnly bool) *ui.Element {
 	k := Tokens(c)