Introduce the `FunctionId` newtype for ids pointing to functions
Introduce the `FunctionId` newtype for ids pointing to functions

rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen