feat(xml): add the basics of declarative XML support

examples/others/xml/lv_example_xml_1.c

@@ -0,0 +1,37 @@
+#include "../../lv_examples.h"
+#if LV_BUILD_EXAMPLES && LV_USE_XML
+
+void lv_example_xml_1(void)
+{
+    lv_xml_component_register_from_file("A:lvgl/examples/others/xml/my_h3.xml");
+    lv_xml_component_register_from_file("A:lvgl/examples/others/xml/my_card.xml");
+    lv_xml_component_register_from_file("A:lvgl/examples/others/xml/my_button.xml");
+    lv_xml_component_register_from_file("A:lvgl/examples/others/xml/view.xml");
+
+    lv_obj_t * obj = lv_xml_create(lv_screen_active(), "view", NULL);
+    lv_obj_set_pos(obj, 10, 10);
+
+    const char * my_button_attrs[] = {
+        "x", "10",
+        "y", "-10",
+        "align", "bottom_left",
+        "btn_text", "New button",
+        NULL, NULL,
+    };
+
+    lv_xml_component_unregister("my_button");
+
+    lv_xml_create(lv_screen_active(), "my_button", my_button_attrs);
+
+    const char * slider_attrs[] = {
+        "x", "200",
+        "y", "-15",
+        "align", "bottom_left",
+        "value", "30",
+        NULL, NULL,
+    };
+
+    lv_obj_t * slider = lv_xml_create(lv_screen_active(), "lv_slider", slider_attrs);
+    lv_obj_set_width(slider, 100);
+}
+#endif