Fix Path tool behavior with Shift-dragging an already selected point, where it wrongly got deselected (#2395)

* Send path tool FSM to Dragging state on MouseDown if clicking selected point

* Cleanup

* Store selected point state before new selection is made and setup deselect logic

* update previously saved point data on every point selection

* Decide whether to deselect or select on extended_select if node not already selected,  when DragStop state is reached instead of inside the  mouse_down function.

* Fix broken merge and remove leftover debug statements

* Code review

---------

Co-authored-by: Keavon Chambers <keavon@keavon.com>

editor/src/messages/tool/common_functionality/shape_editor.rs

@@ -388,6 +388,37 @@ impl ShapeState {
 		None
 	}
 
+	pub fn get_point_selection_state(&mut self, network_interface: &NodeNetworkInterface, mouse_position: DVec2, select_threshold: f64) -> Option<(bool, Option<SelectedPointsInfo>)> {
+		if self.selected_shape_state.is_empty() {
+			return None;
+		}
+
+		if let Some((layer, manipulator_point_id)) = self.find_nearest_point_indices(network_interface, mouse_position, select_threshold) {
+			let vector_data = network_interface.compute_modified_vector(layer)?;
+			let point_position = manipulator_point_id.get_position(&vector_data)?;
+
+			let selected_shape_state = self.selected_shape_state.get(&layer)?;
+			let already_selected = selected_shape_state.is_selected(manipulator_point_id);
+
+			// Offset to snap the selected point to the cursor
+			let offset = mouse_position - network_interface.document_metadata().transform_to_viewport(layer).transform_point2(point_position);
+
+			// Gather current selection information
+			let points = self
+				.selected_shape_state
+				.iter()
+				.flat_map(|(layer, state)| state.selected_points.iter().map(|&point_id| ManipulatorPointInfo { layer: *layer, point_id }))
+				.collect();
+
+			let selection_info = SelectedPointsInfo { points, offset, vector_data };
+
+			// Return the current selection state and info
+			return Some((already_selected, Some(selection_info)));
+		}
+
+		None
+	}
+
 	pub fn select_anchor_point_by_id(&mut self, layer: LayerNodeIdentifier, id: PointId, extend_selection: bool) {
 		if !extend_selection {
 			self.deselect_all_points();