ibus-engines.typing-booster: init at 2.1.1

This package providesa completion input method for faster typing.
See https://mike-fabian.github.io/ibus-typing-booster

Detailed instructions how to activate this IBus engine on your desktop
can be found in the upstream docs: https://mike-fabian.github.io/ibus-typing-booster/documentation.html

A simple VM with the Gnome3 desktop and activated `ibus' looks like
this:

```nix
{
  emojipicker = { pkgs, ... }: {
    services.xserver = {
      enable = true;
      desktopManager.gnome3.enable = true;
      desktopManager.xterm.enable = false;
    };
    users.extraUsers.vm = {
      password = "vm";
      isNormalUser = true;
    };
    i18n.inputMethod.ibus.engines = [
      pkgs.ibus-engines.typing-booster
    ];
    i18n.inputMethod.enabled = "ibus";
    virtualisation.memorySize = 2048;
  };
}
```

Fixes #38721