Reconsider using .rustified_enum() for bindings generation

[FreezyLemon]

Due to the ability of enums in C to be treated as basically just an integer with some predefined constants, it's probably not a good idea to treat all of the FFmpeg enums as Rust enums. Rust enums are a lot stricter and there is probably a decent amount of UB in the crate because of .rustifed_enum() atm. They should almost definitely use newtypes around integers for the bindings, and then enums or bitflags structs on the Rust side.