Note when a a move/borrow error is caused by a deref coercion

Fixes #73268

When a deref coercion occurs, we may end up with a move error if the
base value has been partially moved out of. However, we do not indicate
anywhere that a deref coercion is occuring, resulting in an error
message with a confusing span.

This PR adds an explicit note to move errors when a deref coercion is
involved. We mention the name of the type that the deref-coercion
resolved to, as well as the `Deref::Target` associated type being used.

compiler/rustc_mir/src/util/find_self_call.rs

@@ -1,30 +1,31 @@
 use rustc_middle::mir::*;
+use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::def_id::DefId;
 
 /// Checks if the specified `local` is used as the `self` prameter of a method call
 /// in the provided `BasicBlock`. If it is, then the `DefId` of the called method is
 /// returned.
-pub fn find_self_call(
-    tcx: TyCtxt<'_>,
-    body: &Body<'_>,
+pub fn find_self_call<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
     local: Local,
     block: BasicBlock,
-) -> Option<DefId> {
+) -> Option<(DefId, SubstsRef<'tcx>)> {
     debug!("find_self_call(local={:?}): terminator={:?}", local, &body[block].terminator);
     if let Some(Terminator { kind: TerminatorKind::Call { func, args, .. }, .. }) =
         &body[block].terminator
     {
         debug!("find_self_call: func={:?}", func);
         if let Operand::Constant(box Constant { literal: ty::Const { ty, .. }, .. }) = func {
-            if let ty::FnDef(def_id, _) = *ty.kind() {
+            if let ty::FnDef(def_id, substs) = *ty.kind() {
                 if let Some(ty::AssocItem { fn_has_self_parameter: true, .. }) =
                     tcx.opt_associated_item(def_id)
                 {
                     debug!("find_self_call: args={:?}", args);
                     if let [Operand::Move(self_place) | Operand::Copy(self_place), ..] = **args {
                         if self_place.as_local() == Some(local) {
-                            return Some(def_id);
+                            return Some((def_id, substs));
                         }
                     }
                 }