Auto merge of #12756 - y21:assigning_clones_lifetimes, r=Alexendoo

Avoid emitting `assigning_clones` when cloned data borrows from the place to clone into

Fixes #12444
Fixes #12460
Fixes #12749
Fixes #12757
Fixes #12929

I think the documentation for the function should describe what- and how this is fixing the issues well.
It avoids emitting a warning when the data being cloned borrows from the place to clone into, which is information that we can get from `PossibleBorrowerMap`. Unfortunately, it is a tiny bit tedious to match on the MIR like that and I'm not sure if this is possibly relying a bit too much on the exact MIR lowering for assignments.

Things left to do:
- [x] Handle place projections (or verify that they work as expected)
- [x] Handle non-`Drop` types

changelog: [`assigning_clones`]: avoid warning when the suggestion would lead to a borrow-check error

clippy_utils/src/mir/possible_borrower.rs

@@ -69,7 +69,7 @@ impl<'a, 'b, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'b,
     fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) {
         let lhs = place.local;
         match rvalue {
-            mir::Rvalue::Ref(_, _, borrowed) => {
+            mir::Rvalue::Ref(_, _, borrowed) | mir::Rvalue::CopyForDeref(borrowed) => {
                 self.possible_borrower.add(borrowed.local, lhs);
             },
             other => {