`header_contents` requires providing a header file extension in `name` argument

The below code fails because the name provided to the header_contents method doesn't have a valid c header file extension:

fn main() {
    bindgen::builder()
        .header_contents("input", "") // empty header
        .generate()
        .expect("Unable to generate bindings");
}

The docs don't mention this requirement and the error it creates doesn't actually say that this is the problem:

thread 'main' panicked at D:\.tools\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bindgen-0.69.4\ir\context.rs:556:15:
  libclang error; possible causes include:
  - Invalid flag syntax
  - Unrecognized flags
  - Invalid flag arguments
  - File I/O errors
  - Host vs. target architecture mismatch
  If you encounter an error missing from this list, please file an issue or a PR!
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I assumed that since the argument was name and since the docs didn't mention anything, that it would automatically append an appropriate file extension. I think the error should probably be updated and the docs too maybe.

Start with the Builder::header_contents documentation and the failure reported at ir/context.rs:556. Reproduce the example using an empty header and the name "input" to confirm the behavior and message. Done means the extension requirement is documented and the resulting error clearly identifies this problem.