Use more `Result<T>` for bridge functions to capture C++ exceptions

[ciscorn]

Some bridge functions already return Result<T> so that cxx catches C++ exceptions (e.g. style_add_layer, style_add_source, style_add_image, GeoJson parse / stringify).

However many functions in bridge.rs return plain T rather than Result<T>, so any C++ exception thrown by MapLibre Native aborts the host process.