Update to clap 3.* (#4082)

* Update to clap 3.0

This commit migrates all CLI commands internally used in this project
from structopt/clap2 to clap 3. The intent here is to ensure that we're
using maintained versions of the dependencies as structopt and clap 2
are less maintained nowadays. Most transitions were pretty
straightforward and mostly dealing with structopt/clap3 differences.

* Fix a number of `cargo deny` errors

This commit fixes a few errors around duplicate dependencies which
arose from the prior update to clap3. This also uses a new feature in
`deny.toml`, `skip-tree`, which allows having a bit more targeted
ignores for skips of duplicate version checks. This showed a few more
locations in Wasmtime itself where we could update some dependencies.

crates/wiggle/generate/src/lib.rs

@@ -7,7 +7,7 @@ mod names;
 mod types;
 pub mod wasmtime;
 
-use heck::ShoutySnakeCase;
+use heck::ToShoutySnakeCase;
 use lifetimes::anon_lifetime;
 use proc_macro2::{Literal, TokenStream};
 use quote::quote;