Migrate to C++ 20 & switch to websocketpp develop branch (#4252)

* feat: c++ 20

* fix: c++ 20 deprecations

* fix(msvc): warnings

* chore: add changelog entry

* fix: formatting

* Update websocketpp to the `develop` branch

* Specify other template type in FlagsEnum != operator

* Remove the user of simple template ids in our websocketpp template class

Also standardizes the file a bit by using nested namespaces, using
pragma once

* fix: turn `MAGIC_MESSAGE_SUFFIX` into a `QString`

* hacky unhacky hacky const char hack

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/providers/liveupdates/BasicPubSubManager.hpp

@@ -204,8 +204,8 @@ private:
 
         this->clients_.emplace(hdl, client);
 
-        auto pendingSubsToTake = (std::min)(this->pendingSubscriptions_.size(),
-                                            client->maxSubscriptions);
+        auto pendingSubsToTake = std::min(this->pendingSubscriptions_.size(),
+                                          client->maxSubscriptions);
 
         qCDebug(chatterinoLiveupdates)
             << "LiveUpdate connection opened, subscribing to"