chore: Switch to Rust 2021 edition

Part-of: <https://gitlab.gnome.org/GNOME/fractal/-/merge_requests/1176>

Cargo.toml

@@ -2,7 +2,7 @@
 name = "fractal"
 version = "5.0.0-alpha1"
 authors = ["Julian Sparber <julian@sparber.net>"]
-edition = "2018"
+edition = "2021"
 rust-version = "1.60"
 
 [profile.release]

src/contrib/qr_code.rs

@@ -1,6 +1,5 @@
 // Taken from https://gitlab.gnome.org/msandova/trinket/-/blob/master/src/qr_code.rs
 // All credit goes to Maximiliano
-use std::convert::TryFrom;
 
 use gtk::{glib, prelude::*, subclass::prelude::*};
 

src/login/idp_button.rs

@@ -1,5 +1,3 @@
-use std::convert::{TryFrom, TryInto};
-
 use gtk::{self, glib, glib::clone, prelude::*, subclass::prelude::*, CompositeTemplate};
 use matrix_sdk::ruma::api::client::session::get_login_types::v3::{
     IdentityProvider, IdentityProviderBrand,

src/session/content/explore/public_room_list.rs

@@ -1,5 +1,3 @@
-use std::convert::TryFrom;
-
 use gtk::{gio, glib, glib::clone, prelude::*, subclass::prelude::*};
 use log::error;
 use matrix_sdk::ruma::{

src/session/content/room_details/member_page/mod.rs

@@ -71,8 +71,6 @@ mod imp {
             });
 
             klass.install_action("members.subpage", Some("u"), move |widget, _, param| {
-                use std::convert::TryFrom;
-
                 let state = param
                     .and_then(|variant| variant.get::<u32>())
                     .and_then(|u| Membership::try_from(u).ok());

src/session/mod.rs

@@ -10,7 +10,7 @@ mod sidebar;
 mod user;
 pub mod verification;
 
-use std::{collections::HashSet, convert::TryFrom, fs, path::PathBuf, time::Duration};
+use std::{collections::HashSet, fs, path::PathBuf, time::Duration};
 
 use adw::subclass::prelude::BinImpl;
 use futures::StreamExt;

src/session/room/room_type.rs

@@ -1,4 +1,4 @@
-use std::{convert::TryFrom, fmt};
+use std::fmt;
 
 use gtk::glib;
 use num_enum::{IntoPrimitive, TryFromPrimitive};

src/session/sidebar/category.rs

@@ -7,7 +7,7 @@ use crate::session::{
 };
 
 mod imp {
-    use std::{cell::Cell, convert::TryFrom};
+    use std::cell::Cell;
 
     use once_cell::unsync::OnceCell;
 

src/session/sidebar/mod.rs

@@ -42,10 +42,7 @@ use crate::{
 };
 
 mod imp {
-    use std::{
-        cell::{Cell, RefCell},
-        convert::TryFrom,
-    };
+    use std::cell::{Cell, RefCell};
 
     use glib::{signal::SignalHandlerId, subclass::InitializingObject};
     use once_cell::{sync::Lazy, unsync::OnceCell};

src/session/sidebar/row.rs

@@ -1,5 +1,3 @@
-use std::convert::TryFrom;
-
 use adw::{prelude::*, subclass::prelude::*};
 use gtk::{gdk, glib, glib::clone};
 

src/utils.rs

@@ -166,7 +166,7 @@ macro_rules! _add_toast {
     }};
 }
 
-use std::{convert::TryInto, path::PathBuf, str::FromStr};
+use std::{path::PathBuf, str::FromStr};
 
 use gettextrs::gettext;
 use gtk::{