LibCore+Everywhere: Return ErrorOr from ConfigFile factory methods

I've attempted to handle the errors gracefully where it was clear how to
do so, and simple, but a lot of this was just adding
`release_value_but_fixme_should_propagate_errors()` in places.

Userland/Utilities/keymap.cpp

@@ -53,7 +53,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         return 0;
     }
 
-    auto mapper_config(Core::ConfigFile::open("/etc/Keyboard.ini", Core::ConfigFile::AllowWriting::Yes));
+    auto mapper_config = TRY(Core::ConfigFile::open("/etc/Keyboard.ini", Core::ConfigFile::AllowWriting::Yes));
 
     int rc = 0;