Update edition to 2021

- Remove TryFrom/Into and FromIterator imports
- Prevent impl_validator_using_provider macro in sasl crate from
  constructing trait object

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

Cargo.toml

@@ -7,6 +7,7 @@ members = [  # alphabetically sorted
   "tokio-xmpp",
   "xmpp",
 ]
+resolver = "2"
 
 [patch.crates-io]
 jid = { path = "jid" }