Move some utils out of rustc_const_eval

This allows us to get rid of the `rustc_const_eval->rustc_borrowck`
dependency edge which was delaying the compilation of borrowck.

The added utils in `rustc_middle` are small and should not affect
compile times there.

compiler/rustc_middle/src/util/mod.rs

@@ -0,0 +1,7 @@
+pub mod bug;
+pub mod call_kind;
+pub mod common;
+pub mod find_self_call;
+
+pub use call_kind::{call_kind, CallDesugaringKind, CallKind};
+pub use find_self_call::find_self_call;