Add datetime components 196-215; Kit.At; inert stepper arrows

Calendars, date and time inputs, pickers, clocks, timers, a sun dial,
a season wheel, an agenda and a day schedule. Kit.At rebuilds at a
moment (relative times, midnight). Stepper and NumberInput arrows stop
under Inert. DateInput parks a popup focus as its own.

overlay/bubbles_test.go

@@ -194,3 +194,20 @@ func TestPopoverRefusesNegativeWidth(t *testing.T) {
 		overlay.Popover(c, "X", b.Element, &open, overlay.PopoverOptions{Width: -1}, func() {})
 	})
 }
+
+func TestPopconfirmParksFocusAsItTurnsOff(t *testing.T) {
+	disabled := false
+	tt := view(640, 400, newClock(), false, func(c *ui.Context) {
+		ui.Column(c).Padding(40).Children(func() {
+			overlay.Popconfirm(c, "SELL", "Sell?", overlay.PopconfirmOptions{Disabled: disabled})
+			pixel.Text(c, "elsewhere", pixel.TextOptions{})
+		})
+	})
+	click(t, tt, "SELL")
+	tt.Key(0, ui.KeyTab)
+	disabled = true
+	tt.Frame()
+	if tt.Focused("SELL") && !tt.Focused("elsewhere") {
+		t.Fatal("the focus came back to the button as it turned off")
+	}
+}

overlay/popconfirm.go

@@ -31,8 +31,11 @@ func Popconfirm(c *ui.Context, text, question string, o PopconfirmOptions) Popco
 	if b.Clicked {
 		*open = true
 	}
-	// A popup above a veil closes with its control.
+	// A popup above a veil closes with it, focus parked.
 	if o.Disabled || pixel.Current(c).Inert {
+		if *open {
+			c.Root().Focus()
+		}
 		*open = false
 	}
 	was := *open