message: `zt` and `zb` in Visual modes
  Fixes
diff: @@ -958,7 +958,7 @@ class CommandCenterScrollFirstChar extends BaseCommand {
  @RegisterAction
  class CommandTopScroll extends BaseCommand {
  - modes = [Mode.Normal];
  + modes = [Mode.Normal, Mode.Visual, Mode.VisualLine, Mode.VisualBlock];
  keys = ['z', 't'];
  preservesDesiredColumn() {
  @@ -1016,7 +1016,7 @@ class CommandTopScrollFirstChar extends BaseCommand {
  @RegisterAction
  class CommandBottomScroll extends BaseCommand {
  - modes = [Mode.Normal];
  + modes = [Mode.Normal, Mode.Visual, Mode.VisualLine, Mode.VisualBlock];
  keys = ['z', 'b'];
  preservesDesiredColumn() {
  