Moved to lvgl 9.4 because 9.5 has removed runtime xml support.

Made basic example of editing xml layout from backend.

Provider/main/device.hpp

@@ -7,6 +7,12 @@
 constexpr int MAX_DEVICES = 8;
 constexpr int DEVICE_XML_MAX = 2048;
 
+constexpr char kDefaultLayoutXml[] = 
+    "<lv_obj width=\"800\" height=\"480\" flex_flow=\"column\" flex_main_place=\"center\" flex_cross_place=\"center\" style_pad_row=\"10\">\n"
+    "    <lv_label text=\"Hello World\" />\n"
+    "    <lv_label bind_text=\"device_mac\" />\n"
+    "</lv_obj>";
+
 struct device_t
 {
   char mac[18];               // "AA:BB:CC:DD:EE:FF\0"