Add files components 406-420; Tree opens to a known choice

Fifteen file components: FileExplorer, FileGrid, FileIcon, PathBar,
MemoryCard, DiskUsage, UploadQueue, Trash, RecentFiles, FilePreview,
ArchiveViewer, FileDetails, SharePanel, SyncStatus and QuotaMeter.

FileIcon draws six kinds as hand-placed 12x12 pages and a folder. The
browsers build on data.Tree, List, GridView and Table; ArchiveViewer
owns its sort and keeps the caller's index on its entry. UploadQueue
keys rows by name so focus stays on its row. SharePanel never logs the
link. SyncStatus turns its arrows on Busy steps, so syncing moves under
Reduce Motion.

data.Tree now opens the closed branches above a chosen path it knows,
so a caller's starting path survives the first frame.

data/treevalue_test.go

@@ -38,3 +38,14 @@ func TestTreeDrawsValuesInTheirSlot(t *testing.T) {
 		t.Fatalf("choosing hp (%q) did not swap which value is inked", sel)
 	}
 }
+
+func TestTreeRevealsAChoiceInAClosedBranch(t *testing.T) {
+	// Ether sits in Bag, which starts closed.
+	sel := "0/1"
+	tt := view(400, 300, newClock(), false, func(c *ui.Context) {
+		data.Tree(c, "Items", bag, &sel, data.TreeOptions{})
+	})
+	if r := find(t, tt, "Items"); sel != "0/1" || r.H != 4*2*pixel.LineHeight {
+		t.Fatalf("the choice became %q in %v, want Bag opened on Ether", sel, r)
+	}
+}