Notify about a new touch down event.
The `(x, y)` position represents the new touch point position in the streams logical coordinate space.
May only be called on a remote desktop session with `XDP_DEVICE_TOUCHSCREEN` access.
| this |
a [class@Session] |
| stream |
the node ID of the pipewire stream the position is relative to |
| slot |
touch slot where the touch point appeared |
| x |
new X position |
| y |
new Y position |