Derive Var and Export for DynGd<T, D>

- Formatting fixes - use newline to seperate steps in given testcase

itest/godot/ManualFfiTests.gd

@@ -70,14 +70,16 @@ func test_export():
 
 func test_export_dyn_gd():
 	var dyn_gd_exporter = DynGdExporter.new()
-	# Nodehealth is valid candidate both for `empty` and `second` fields.
+
+	# NodeHealth is valid candidate both for `empty` and `second` fields.
 	var node = NodeHealth.new()
 	dyn_gd_exporter.first = node
 	assert_eq(dyn_gd_exporter.first, node)
+
 	dyn_gd_exporter.second = node
 	assert_eq(dyn_gd_exporter.second, node)
 
-	# RefcHealth is valid candidate for `first` field
+	# RefcHealth is valid candidate for `first` field.
 	var refc = RefcHealth.new()
 	dyn_gd_exporter.first = refc
 	assert_eq(dyn_gd_exporter.first, refc)
@@ -87,9 +89,11 @@ func test_export_dyn_gd():
 func test_export_dyn_gd_should_fail_for_wrong_type():
 	var dyn_gd_exporter = RcDynGdExporter.new()
 	var refc = RefcHealth.new()
+
 	disable_error_messages()
 	dyn_gd_exporter.only_node_health = refc # Should fail.
 	enable_error_messages()
+
 	assert_fail("`DynGdExporter.only_node_health` should only accept NodeHealth if it implements InstanceIdProvider trait")
 
 class MockObjGd extends Object: