Determine call type based on `LanguageItems`

[JustusAdam]

This changes the way that std::ops::Fn::call and std::future::Future::poll is detected in pdg construction to use the LangaugeItems struct which I think is the way it's supposed to be done.

In addition it will also now detect FnMut:call_mut and FnOnce::call_once now.

I haven't added test cases for the last two. Are there test cases for Fn::call that I could model off of?

[JustusAdam]

I don't understand why this CI fails btw. This doesn't seem to have anything to do with my changes