Add chat components 321-345; named List rows, inert scroll views

Speech bubbles, a chat log that follows its end, a composer that sends
on Enter, typing dots, chat and channel lists, read receipts,
reactions, emoji and sticker pickers, mentions, date and unread rules,
system lines, member lists, user cards, a mailbox, mail reader and
letter, a notification bell, call controls, a voice meter, attachment
chips, link previews and polls.

pixel's editor takes EnterSends; display's Bubble takes a Fill and
exports EmojiSprite. data.List names its rows, which also lets typing
choose one. layout.ScrollArea and input.TextArea hold still under
Inert, and an inert scroll view leaves the Tab order until it wakes.

layout/scrollarea.go

@@ -44,21 +44,28 @@ func ScrollArea(c *ui.Context, s *ui.ScrollState, o ScrollAreaOptions, children
 	row := ui.Row(c).AlignItems(ui.Stretch).Reverse()
 	last := ui.Local(row, scrollKey{}, func() float32 { return s.Y })
 	view := row.Bounds().H
-	// Disabled freezes the view: any move is undone before paint.
-	if o.Disabled {
+	// Off freezes the view: any move is undone before paint.
+	inert := pixel.Current(c).Inert
+	if o.Disabled || inert {
 		s.Y = *last
 	}
 	var v *ui.Element
 	row.Children(func() {
-		scrollBar(c, k, s, view, o.Disabled)
+		scrollBar(c, k, s, view, o.Disabled || inert, o.Disabled)
 		// A disabled view is a new element; the focus leaves.
 		v = ui.Scroll(c).Key(o.Disabled).TrackScroll(s).Grow(1).Label(o.Label).FocusRing(false)
-		if o.Disabled {
+		switch {
+		case o.Disabled:
 			v.Role(ui.RoleGroup).Description(k.Msg("disabled"))
-		} else {
+		case inert:
+			// Out of the Tab order, so Tab moves past it.
+			v.Role(ui.RoleScroll)
+		default:
 			v.Role(ui.RoleScroll).Focusable()
 		}
 		v.Children(children)
+		// Inert parks the focus and gives it back after.
+		pixel.Park(c, v, inert)
 	})
 	focus := v.FocusVisible()
 	row.Draw(func(p *ui.Painter, r ui.Rect) {
@@ -83,11 +90,11 @@ func ScrollArea(c *ui.Context, s *ui.ScrollState, o ScrollAreaOptions, children
 	return res
 }
 
-// scrollBar draws arrows, track and thumb, and moves s.
-func scrollBar(c *ui.Context, k pixel.Kit, s *ui.ScrollState, view float32, disabled bool) {
+// scrollBar moves s unless off; dim draws it disabled.
+func scrollBar(c *ui.Context, k pixel.Kit, s *ui.ScrollState, view float32, disabled, dim bool) {
 	clamp := func(y float32) { s.Y = max(0, min(y, s.MaxY)) }
 	ui.Column(c).Width(k.D(barW)).DrawOver(func(p *ui.Painter, r ui.Rect) {
-		if disabled {
+		if dim {
 			g := k.Canvas(p, r)
 			g.Checker(0, 0, g.W, g.H, pixel.Face)
 		}