cleanup: Prefer template strings

Template strings are much nicer than string concatenation, so use
them where possible; this excludes translatable strings and any
strings containing '/' (until we can depend on gettext >= 0.20[0]).

[0] https://savannah.gnu.org/bugs/?50920

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/612

js/misc/inputMethod.js

@@ -262,7 +262,7 @@ class InputMethod extends Clutter.InputMethod {
                                                       let retval = context.process_key_event_async_finish(res);
                                                       this.notify_key_event(event, retval);
                                                   } catch (e) {
-                                                      log('Error processing key on IM: ' + e.message);
+                                                      log(`Error processing key on IM: ${e.message}`);
                                                   }
                                               });
         return true;