vfmt: add _keep.vv tests for the recent fixes, to prevent regressions

vlib/v/fmt/tests/c_struct_init_keep.vv

@@ -0,0 +1,30 @@
+module main
+
+fn abc() {
+	desc := C.sapp_desc{
+		width: a.width
+		height: a.height
+		user_data: &a
+		init_userdata_cb: init
+		frame_userdata_cb: frame
+		event_userdata_cb: event
+		window_title: title.str
+		html5_canvas_name: title.str
+		cleanup_userdata_cb: cleanup
+	}
+}
+
+fn init(user_data voidptr) {
+	desc := C.sg_desc{
+		mtl_device: sapp.metal_get_device()
+		mtl_renderpass_descriptor_cb: sapp.metal_get_renderpass_descriptor
+		mtl_drawable_cb: sapp.metal_get_drawable
+		d3d11_device: sapp.d3d11_get_device()
+		d3d11_device_context: sapp.d3d11_get_device_context()
+		d3d11_render_target_view_cb: sapp.d3d11_get_render_target_view
+		d3d11_depth_stencil_view_cb: sapp.d3d11_get_depth_stencil_view
+	}
+	sgl_desc := C.sgl_desc_t{
+		max_vertices: 50 * 65536
+	}
+}

vlib/v/fmt/tests/enum_comments_keep.vv

@@ -0,0 +1,17 @@
+module main
+
+// Top level comment
+enum EnumType {
+	// comment for the enum
+	abc
+	xyz // comment for the enum field
+}
+
+// Another top level comment
+enum PacketType {
+	// Regular data packet
+	data // abc def
+	// xyz
+	// another comment
+	abcd // jklmn
+}

vlib/v/fmt/tests/ref_type_cast_keep.vv

@@ -0,0 +1,9 @@
+module main
+
+fn cleanup(user_data voidptr) {
+	abc := App(user_data)
+	xyz := &App(user_data)
+	//
+	mut app := App(user_data)
+	mut ref := &App(user_data)
+}