extensions CHANGE compile internal plugins separately

Avoid including *.c files into other c file and let them compile
individualy. The change needs also to correct includes in the plugins
source codes.
diff --git a/src/plugins_exts_yangdata.c b/src/plugins_exts_yangdata.c
index 180de16..3742a2b 100644
--- a/src/plugins_exts_yangdata.c
+++ b/src/plugins_exts_yangdata.c
@@ -12,13 +12,13 @@
  *     https://opensource.org/licenses/BSD-3-Clause
  */
 
+#include <stdint.h>
 #include <stdlib.h>
+#include <string.h>
 
+#include "libyang.h"
 #include "plugins_exts.h"
 
-#include "tree_edit.h"
-#include "tree_schema.h"
-
 /**
  * @brief Storage for ID used to check plugin API version compatibility.
  * Ignored here in the internal plugin.