feat: changed startNode to use custom type for data

changed to startNode file to be a general file for custom node types, and created a custom type for the data property of StartNode.

BREAKING: renamed StartNode.tsx to NodeDefinitions.tsx

ref: N25B-114

src/visualProgrammingUI/VisProgUI.tsx

@@ -17,7 +17,7 @@ import {
     type Connection,
 } from '@xyflow/react';
 import '@xyflow/react/dist/style.css';
-import StartNode from './components/StartNode.tsx';
+import StartNode from "./components/NodeDefinitions.tsx";
 
 const nodeTypes = {
     startNode: StartNode,
@@ -28,7 +28,7 @@ const initialNodes = [
         id: 'start',
         type: 'startNode',
         position: {x: 0, y: 0},
-        data: {label: 'Start'},
+        data: {label: 'start'}
     },
     {
         id: 'genericPhase',