ufbt: fixed FAP_SRC_DIR (#2970)

* fbt, ufbt: fixed "_appdir" internal property and FAP_SRC_DIR not working in ufbt environment
* fbt, ufbt: reworked CompileIcons(); added app's own root to app's #include path
* fbt: cleaner resolve_real_dir_node

Co-authored-by: あく <alleteam@gmail.com>

scripts/fbt/appmanifest.py

@@ -2,6 +2,7 @@ import os
 import re
 from dataclasses import dataclass, field
 from enum import Enum
+from fbt.util import resolve_real_dir_node
 from typing import Callable, ClassVar, List, Optional, Tuple, Union
 
 
@@ -152,7 +153,7 @@ class AppManager:
                 FlipperApplication(
                     *args,
                     **kw,
-                    _appdir=app_dir_node,
+                    _appdir=resolve_real_dir_node(app_dir_node),
                     _apppath=os.path.dirname(app_manifest_path),
                     _appmanager=self,
                 ),