feat: ic-cdk-bindgen replace import macro

[chenyan-dfinity]

Work with dfinity/candid#422

Proposed workflow:

• Canister project add ic-cdk-bindgen as a build dependency that generates Rust bindings in the source directory with config options

use ic_cdk_bindgen::{Builder, Config};
fn main() {
    let counter = Config::new("counter");
    let mut builder = Builder::new();
    builder.add(counter);
    builder.build(None);  // default write to src/declarations
}

• In the canister code,

mod declarations;
use declarations::counter::counter;

counter.inc().await?