Add TYPE_TEXT_VARIATION_VISIBLE_PASSWORD for Android keyboard

Currently there is no way to set keyboard to this type. But it holds many advantages: no autocomplete, immediate text events. Everything you need for a in-game input. I had to resolve to write my own wrapper because of this. There are keyboards which use some popular autocomplete features extensively, but this makes keyboard very hard to use in game.

The constant is TYPE_TEXT_VARIATION_VISIBLE_PASSWORD.

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On the side note, it would be great to be able to just set any constant to setImeOptions/setInputType. Or to have callback with EditText, where one could set all options needed.