Move a lot of rustc_query_system::plumbing to rustc_query_impl::execution (part 1).

[Note: this commit conceptually moves 75% of a file to another location,
and leaves 25% of it behind. It's impossible to preserve all the git
history. To preserve git history of the moved 75%, in this commit we
rename the file and remove the 25% from it, leaving the code in an
incomplete (uncompilable) state. In the next commit we add back the
25% in the old location.]

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_impl`. This commit does some of that.

Mostly it's just moving code from one file to a new file. 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.

compiler/rustc_query_system/src/lib.rs

@@ -1,7 +1,6 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![feature(assert_matches)]
-#![feature(core_intrinsics)]
 #![feature(min_specialization)]
 // tidy-alphabetical-end