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.

src/commands/settings.rs

@@ -1,17 +1,17 @@
 //! The module that implements the `wasmtime settings` command.
 
 use anyhow::{anyhow, Result};
+use clap::Parser;
 use std::collections::BTreeMap;
 use std::str::FromStr;
-use structopt::StructOpt;
 use wasmtime_environ::{FlagValue, Setting, SettingKind};
 
 /// Displays available Cranelift settings for a target.
-#[derive(StructOpt)]
-#[structopt(name = "run")]
+#[derive(Parser)]
+#[clap(name = "run")]
 pub struct SettingsCommand {
     /// The target triple to get the settings for; defaults to the host triple.
-    #[structopt(long, value_name = "TARGET")]
+    #[clap(long, value_name = "TARGET")]
     target: Option<String>,
 }