Move a lot of rustc_query_system::plumbing to rustc_query_info::plumbing.

We are in the process of eliminating `rustc_query_system`. Chunks of it
are unused by `rustc_middle`, and so can be moved into
`rustc_query_info`. This commit does some of that.

Mostly it's just moving code from one file to another. There are a
couple of non-trivial changes.

- `QueryState` and `ActiveKeyStatus` must remain in `rustc_query_system`
  because they are used by `rustc_middle`. But their inherent methods
  are not used by `rustc_middle`. So these methods are moved and
  converted to free functions.

- The visibility of some things must increase. This includes `DepGraphData`
  and some of its methods, which are now used in `rustc_query_impl`.
  This is a bit annoying but seems hard to avoid.

What little is left behind in
`compiler/rustc_query_system/src/query/plumbing.rs` will be able to
moved into `rustc_query_impl` or `rustc_middle` in the future.

Author: nnethercote

compiler/rustc_query_impl/src/lib.rs

@@ -3,6 +3,7 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![feature(adt_const_params)]
+#![feature(core_intrinsics)]
 #![feature(min_specialization)]
 #![feature(rustc_attrs)]
 // tidy-alphabetical-end
@@ -25,7 +26,7 @@ use rustc_query_system::dep_graph::SerializedDepNodeIndex;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_query_system::query::{
     CycleError, CycleErrorHandling, HashResult, QueryCache, QueryDispatcher, QueryMap, QueryMode,
-    QueryState, get_query_incr, get_query_non_incr,
+    QueryState,
 };
 use rustc_span::{ErrorGuaranteed, Span};