Take care of scroll divisor remainders for PS/2 drag scroll (qmk#20732)

Author: dkao

drivers/ps2/ps2_mouse.c

@@ -265,20 +265,27 @@ static inline void ps2_mouse_scroll_button_task(report_mouse_t *mouse_report) {
         SCROLL_SENT,
     } scroll_state                     = SCROLL_NONE;
     static uint16_t scroll_button_time = 0;
+    static int16_t  scroll_x, scroll_y;
 
     if (PS2_MOUSE_SCROLL_BTN_MASK == (mouse_report->buttons & (PS2_MOUSE_SCROLL_BTN_MASK))) {
         // All scroll buttons are pressed
 
         if (scroll_state == SCROLL_NONE) {
             scroll_button_time = timer_read();
             scroll_state       = SCROLL_BTN;
+            scroll_x           = 0;
+            scroll_y           = 0;
         }
 
         // If the mouse has moved, update the report to scroll instead of move the mouse
         if (mouse_report->x || mouse_report->y) {
-            scroll_state    = SCROLL_SENT;
-            mouse_report->v = -mouse_report->y / (PS2_MOUSE_SCROLL_DIVISOR_V);
-            mouse_report->h = mouse_report->x / (PS2_MOUSE_SCROLL_DIVISOR_H);
+            scroll_state = SCROLL_SENT;
+            scroll_y += mouse_report->y;
+            scroll_x += mouse_report->x;
+            mouse_report->v = -scroll_y / (PS2_MOUSE_SCROLL_DIVISOR_V);
+            mouse_report->h = scroll_x / (PS2_MOUSE_SCROLL_DIVISOR_H);
+            scroll_y += (mouse_report->v * (PS2_MOUSE_SCROLL_DIVISOR_V));
+            scroll_x -= (mouse_report->h * (PS2_MOUSE_SCROLL_DIVISOR_H));
             mouse_report->x = 0;
             mouse_report->y = 0;
 #ifdef PS2_MOUSE_INVERT_H