jb: touch debounce (#798)

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

## Description of change
Debouce option for touch input. Applies to all touch handlers (rawinput,
win8, win7) since it sits at the touch layer, and then consumed by jb
touch logic.

## Testing

src/spice2x/touch/touch.h

@@ -7,6 +7,7 @@ struct TouchPoint {
     DWORD id;
     LONG x, y;
     bool mouse;
+    double down_ms = 0.0; // performance-counter milliseconds when the contact first landed
 };
 enum TouchEventType {
     TOUCH_DOWN,