libspa-sys: Add bindings for format parsing and building functions

Adds spa format parsing and building functions to the sys crate.

I discovered that we can rename the symbol in rust and still link to the actual linker symbol using the #[link_name = "<name>] attribute, so the new symbols have the same name as in the SPA headers now (spa_* instead of libspa_rs_*), and I also changed the already existing names to match, too.

I also had to remove the spa_type_* static variable definitions from the generated bindgen bindings to avoid name collisions, but they were not actually linkable anyways.