chore: add test for ecma private fields & methods

tests/query/highlights/ecma/test.ts

@@ -0,0 +1,25 @@
+class H {
+  pub_field = "Hello";
+  //  ^ property
+
+  #priv_field = "World!";
+  //   ^ property
+
+  #private_method() {
+    //  ^ method
+    return `${this.pub_field} -- ${this.#priv_field}`;
+    //                                      ^ property
+    //                ^ property
+  }
+
+  public_method() {
+    //  ^ method
+    return this.#private_method();
+    //                ^ method
+  }
+
+  ok() {
+    return this.public_method();
+    //                ^ method
+  }
+}