Removes the windows-specific hack from sceCtrl
to read keyboard input and instead add a hack to
PPSSPPWindows.
The input mapping is still hardcoded and is the same
as it was in sceCtrl.
Add an std::list to WindowsHost that, curretly, contains
a hardcoded list of preferred `InputDevice`s. Devices
are tried in-order until one of them reports success.
Xinput is preferred over Keyboard. Keyboard always
returns success. Pointers are stored in the std::list
for polymorphism.
Change XinputDevice to report failure as soon as a
device can't be queried, instead of only a frame later.
