add extra resource path lookups for app files
Add two paths to lookup:
- ":/org.kde.syntax-highlighting/syntax-addons" for definitions
- ":/org.kde.syntax-highlighting/themes-addons" for themes
This allows other libraries & applications to bundle extra definitions or themes inside their resources instead of polluting the global namespace with specialized things.
In addition, only for the internal resource path
":/org.kde.syntax-highlighting/syntax"
the CBOR index loading is used, as only there this makes sense because for all other paths it will prevent that new files can be added, as designed.