Add exec tests

packages/babel-plugin-transform-optional-chaining/test/fixtures/execute/delete.js

@@ -0,0 +1,20 @@
+const obj = {
+  a: {
+    b: 0,
+  },
+};
+
+let test = delete obj?.a?.b;
+assert.equal(obj.a.b, undefined);
+assert.equal(test, true);
+
+test = delete obj?.a.b;
+assert.equal(obj.a.b, undefined);
+assert.equal(test, true);
+
+test = delete obj?.b?.b;
+assert.equal(obj.b, undefined);
+assert.equal(test, undefined);
+
+delete obj?.a;
+assert.equal(obj.a, undefined);