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/layout_test.go

@@ -383,3 +383,70 @@ func boolInt(b bool) int {
 	}
 	return 0
 }
+
+func TestScrollAreaHoldsStillWhenInert(t *testing.T) {
+	s, inert := ui.ScrollState{}, false
+	tt := ui.NewTester(func(c *ui.Context) {
+		pixel.Use(c, pixel.Settings{Palette: pixel.SpringDay, Inert: inert})
+		layout.ScrollArea(c, &s, layout.ScrollAreaOptions{Label: "List"}, func() {
+			for range 40 {
+				ui.Box(c).Height(32)
+			}
+		}).Element.Size(200, 100)
+	}, 300, 200)
+	tt.Frame()
+	r := box(t, tt, "List")
+	if err := tt.Click("List"); err != nil {
+		t.Fatal(err)
+	}
+	bar := func() []uint8 {
+		return tt.Image().SubImage(image.Rect(int(r.X+r.W), int(r.Y), int(r.X+r.W)+20, int(r.Y+r.H))).(*image.RGBA).Pix
+	}
+	looks := bar()
+	inert = true
+	tt.Frame()
+	// Inert keeps the look; only Disabled dims the bar.
+	if string(bar()) != string(looks) {
+		t.Fatal("an inert scroll area changed its look")
+	}
+	// Keys, the wheel and the arrows all leave it be.
+	tt.Key(0, ui.KeyDown)
+	tt.Move(r.X+20, r.Y+30)
+	tt.Scroll(r.X+20, r.Y+30, 0, 80)
+	if err := tt.Click("SCROLL DOWN"); err != nil {
+		t.Fatal(err)
+	}
+	if s.Y != 0 {
+		t.Fatalf("an inert scroll area moved to %v", s.Y)
+	}
+}
+
+func TestInertScrollAreaLetsTabPass(t *testing.T) {
+	s, inert, clicks := ui.ScrollState{}, false, 0
+	tt := ui.NewTester(func(c *ui.Context) {
+		use(c)
+		set := pixel.Current(c)
+		set.Inert = inert
+		pixel.Scope(c, set, func() {
+			layout.ScrollArea(c, &s, layout.ScrollAreaOptions{Label: "List"}, func() {
+				for range 40 {
+					ui.Box(c).Height(32)
+				}
+			}).Element.Size(200, 100)
+		})
+		if ui.ButtonBase(c).Label("Next").Size(60, 20).Clicked() {
+			clicks++
+		}
+	}, 300, 200)
+	if err := tt.Click("List"); err != nil {
+		t.Fatal(err)
+	}
+	inert = true
+	tt.Frame()
+	// Parked on the root, Tab passes the inert view.
+	tt.Key(0, ui.KeyTab)
+	tt.Key(0, ui.KeyEnter)
+	if clicks != 1 {
+		t.Fatal("Tab stuck on an inert scroll area")
+	}
+}