fbt: fixes for ufbt pt3 (#1970)

* fbt: replaced debug dir paths with FBT_DEBUG_DIR
* scripts: updated requirements.txt
* fbt: fixed wrong import
* fbt: removed delayed import for file2image
* fbt: added UPDATE_BUNDLE_DIR internal var
* fbt: cleaner internal management of extapps
* applications: added fap_libs for core apps to link with resources when building with --extra-ext-apps
* fbt: removed deprecation stub for faps
* fbt: added quotation for icons build cmd
* fbt: reworked BUILD_DIR & fap work dir handling; fap debug: using debug elf path from fbt
* fbt: explicit LIB_DIST_DIR

firmware.scons

@@ -20,8 +20,7 @@ env = ENV.Clone(
     BUILD_DIR=fw_build_meta["build_dir"],
     IS_BASE_FIRMWARE=fw_build_meta["type"] == "firmware",
     FW_FLAVOR=fw_build_meta["flavor"],
-    PLUGIN_ELF_DIR="${BUILD_DIR}",
-    LIB_DIST_DIR="${BUILD_DIR}/lib",
+    LIB_DIST_DIR=fw_build_meta["build_dir"].Dir("lib"),
     LINT_SOURCES=[
         "applications",
     ],
@@ -142,12 +141,14 @@ for app_dir, _ in env["APPDIRS"]:
 
 fwenv.PrepareApplicationsBuild()
 
-# Build external apps
+# Build external apps + configure SDK
 if env["IS_BASE_FIRMWARE"]:
-    extapps = fwenv["FW_EXTAPPS"] = SConscript(
-        "site_scons/extapps.scons", exports={"ENV": fwenv}
+    fwenv.SetDefault(FBT_FAP_DEBUG_ELF_ROOT="${BUILD_DIR}/.extapps")
+    fwenv["FW_EXTAPPS"] = SConscript(
+        "site_scons/extapps.scons",
+        exports={"ENV": fwenv},
     )
-    fw_artifacts.append(extapps["sdk_tree"])
+    fw_artifacts.append(fwenv["FW_EXTAPPS"].sdk_tree)
 
 
 # Add preprocessor definitions for current set of apps