Switch from failure to anyhow (#1851)

This commit switches all of `wasm-bindgen` from the `failure` crate to
`anyhow`. The `anyhow` crate should serve all the purposes that we
previously used `failure` for but has a few advantages:

* It's based on the standard `Error` trait rather than a custom `Fail`
  trait, improving ecosystem compatibility.
* We don't need a `#[derive(Fail)]`, which means that's less code to
  compile for `wasm-bindgen`. This notably helps the compile time of
  `web-sys` itself.
* Using `Result<()>` in `fn main` with `anyhow::Error` produces
  human-readable output, so we can use that natively.

crates/cli-support/src/wasm2es6js.rs

@@ -1,4 +1,4 @@
-use failure::{bail, Error};
+use anyhow::{bail, Error};
 use std::collections::HashSet;
 use walrus::Module;