* Move the C++ elements back into private_api (despite being generated), so that struct_name_to_tokens can generate the right name in re_exports
* When generating the llr_Expression::Struct for the path elements, make sure
that all fields are filled out, to avoid an empty value expression in Expression::Struct
in the Rust generator. Since we don't generate tuples but a named struct, we must provide all fields.
This patch takes care of the lowering of events/coordinates arrays as
path data, which originates from a `commands: ...` string of SVG path
commands.
In order to minimize the path specific code in the generator, the
compile_paths now generates a Vec<Expression> for the events and
coordinates.
