Attribute Macro uniffi::constructor

#[constructor]

A dummy macro that does nothing.

This exists so #[uniffi::export] can emit its input verbatim without causing unexpected errors, plus some extra code in case everything is okay.

It is important for #[uniffi::export] to not raise unexpected errors if it fails to parse the input as this happens very often when the proc-macro is run on an incomplete input by rust-analyzer while the developer is typing.