fbt: fixes for ufbt compat (#1940)

* fbt: split sdk management code
* scripts: fixed import handling
* fbt: sdk: reformatted paths
* scrips: dist: bundling libs as a build artifact
* fbt: sdk: better path management
* typo fix
* fbt: sdk: minor path handling fixes
* toolchain: fixed windows toolchain download

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

site_scons/extapps.scons

@@ -21,7 +21,7 @@ appenv = ENV.Clone(
 )
 
 appenv.Replace(
-    LINKER_SCRIPT="application_ext",
+    LINKER_SCRIPT=appenv.subst("$APP_LINKER_SCRIPT"),
 )
 
 appenv.AppendUnique(