preserve per-event mouse coordinates; prefer in ui signal producing codepath

src/os/gfx/os_gfx.h

@@ -71,6 +71,7 @@ struct OS_Event
   B32 right_sided;
   U32 character;
   U32 repeat_count;
+  Vec2F32 pos;
   Vec2F32 delta;
   String8List strings;
 };

src/os/gfx/win32/os_gfx_win32.c

@@ -416,6 +416,8 @@ w32_wnd_proc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
             event->key = OS_Key_RightMouseButton;
           }break;
         }
+        event->pos.x = (F32)LOWORD(lParam);
+        event->pos.y = (F32)HIWORD(lParam);
         if(release)
         {
           ReleaseCapture();