In DSPCore.cpp, there were two `std::fill` uses that could be simplified using `std::fill_n`. Due to their proximity with other `std::fill` algorithms being modernized with ranges, I chose to make these examples into the rare `std::ranges::fill_n`.

ControllerInterface: Adjust sort priorities to ensure default keyboard-mouse device is first.

Enable emulator hotkeys and controller input (when that option is
enabled) when a TAS Input window has focus, as if it was the render
window instead.  This allows TASers to use frame advance and the like
without having to switch the focused window or disabling Hotkeys Require
Window Focus which also picks up keypresses while other apps are active.

Cursor updates are disabled when the TAS Input window has focus, as
otherwise the Wii IR widget (and anything else controlled by the mouse)
becomes unusable. The cursor continues to work normally when the render
window has focus.

This specific issue was already addressed by https://github.com/dolphin-emu/dolphin/pull/11635
though I felt like there was something more we could do, and wasn't too happy with the
likelihood of devices update calls being skipped (due to `m_devices_population_mutex` being locked).

Add hotkey for centering mouse in render window.