nost: touch piano mode (#830)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Touch piano mode. Allows piano keys to be played with the touch screen.
Since the touch screen is still needed for menu navigation (including
during songs) a toggle switch is added so that the user can flip between
navigation mode and piano mode.

The touch targets are pixel-perfect. Don't let the game's piano
animations fool you.

## Testing

src/spice2x/touch/native/nativetouchhook.h

@@ -1,8 +1,23 @@
+#pragma once
+
 #include <windows.h>
 
 namespace nativetouch {
+    struct NativeTouchEvent {
+        DWORD id;
+        LONG x;
+        LONG y;
+        bool down;
+        bool move;
+        bool up;
+        bool synthetic;
+    };
+
+    using TouchInputFilter = bool (*)(const NativeTouchEvent &event);
+
     void hook(HMODULE module);
     void refresh_contact_lifetime();
+    void set_input_filter(TouchInputFilter filter);
 
     // true once hook() has installed the native touch stack for the current game;
     // such games consume touch through the GetTouchInputInfo hook rather than spicetouch