Disable OnScreenKeyboardOverlapsGameWindow on iOS when hardware keyboard is attached

[frenzibyte]

Noticed while working on fixing iOS hardware keyboard issues. When a hardware keyboard is attached, the software keyboard no longer shows and "overlaps with the game window", so it's more ideal for the OnScreenKeyboardOverlapsGameWindow flag to remain false in that case, so that search text boxes on osu! still gain focus when they are present (i.e. when opening song select or opening settings overlay).

An Android companion to this should be in place if this change can be agreed upon.

Also note that this implementation can be simply replaced with !SDL_HasKeyboard(), and we can also just replace these overrides with a single override at SDLGameHost that returns !SDL_HasKeyboard() (usually always false on desktop platforms, and true on mobile platforms if there are no hardware keyboards attached). I can go with that approach if it makes more sense (although I would have to test if it actually works as expected).

[smoogipoo]

can be simply replaced with !SDL_HasKeyboard()

I think this makes sense.

[frenzibyte]

I've went the full route by moving this to SDLGameHost and use SDL_HasKeyboard(), might be good for users on Windows without a keyboard (assuming it works). Tested to show correct behaviour (SDL_HasKeyboard() returns true) on Windows and macOS.

[peppy]

Let's get this in the next(next) release and see how it fares.