Expose Edit Spline in the Modify extension

assets/icons/modify_splinedit.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#B4B6B9" stroke-width="1.4" stroke-linecap="round" stroke-linejoin="round"><path d="M2 18C4 2 13 22 20 5"/><path stroke="#6DB7ED" d="m13 9 6-6 3 3-6 6-4 1Z"/></svg>

src/ui/ribbon/modify_tools/04_splinedit.rs

@@ -0,0 +1,6 @@
+Tool {
+    command: "SPLINEDIT",
+    label: "Edit Spline",
+    icon: include_bytes!(concat!(env!("CARGO_MANIFEST_DIR"), "/assets/icons/modify_splinedit.svg")),
+    options: &[],
+}