fix(web): correct childWithDescendant() functionality

This fix allows for more granular address control when marshalling nodes
across WASM. This is necessary for node methods which accept another
node as a parameter (i.e., `childWithDescendant()`)

lib/binding_web/test/node.test.ts

@@ -189,6 +189,21 @@ describe('Node', () => {
     });
   });
 
+  describe('.childWithDescendant()', () => {
+    it('correctly retrieves immediate children', () => {
+      const sourceCode = 'let x = 1; console.log(x);';
+      tree = parser.parse(sourceCode)!;
+      const root = tree.rootNode
+      const child = root.children[0].children[0]
+      const a = root.childWithDescendant(child)
+      expect(a!.startIndex).toBe(0)
+      const b = a!.childWithDescendant(child)
+      expect(b).toEqual(child)
+      const c = b!.childWithDescendant(child)
+      expect(c).toBeNull()
+    });
+  });
+
   describe('.nextSibling and .previousSibling', () => {
     it('returns the node\'s next and previous sibling', () => {
       tree = parser.parse('x10 + 1000')!;