Make HandleCycleError an enum instead of a macro-generated closure

- Add a `HandleCycleError` enum to rustc_query_system, along with a `handle_cycle_error` function
- Move `Value` to rustc_query_system, so `handle_cycle_error` can use it
- Move the `Value` impls from rustc_query_impl to rustc_middle. This is necessary due to orphan rules.

compiler/rustc_query_impl/src/lib.rs

@@ -34,9 +34,6 @@ pub use rustc_query_system::query::{deadlock, QueryContext};
 mod keys;
 use keys::Key;
 
-mod values;
-use self::values::Value;
-
 pub use rustc_query_system::query::QueryConfig;
 pub(crate) use rustc_query_system::query::{QueryDescription, QueryVTable};