Modify `find_expr` from `Span` to better account for closures

Start pointing to where bindings were declared when they are captured in closures:

```
error[E0597]: `x` does not live long enough
  --> $DIR/suggest-return-closure.rs:23:9
   |
LL |     let x = String::new();
   |         - binding `x` declared here
...
LL |     |c| {
   |     --- value captured here
LL |         x.push(c);
   |         ^ borrowed value does not live long enough
...
LL | }
   | -- borrow later used here
   | |
   | `x` dropped here while still borrowed
```

Suggest cloning in more cases involving closures:

```
error[E0507]: cannot move out of `foo` in pattern guard
  --> $DIR/issue-27282-move-ref-mut-into-guard.rs:11:19
   |
LL |             if { (|| { let mut bar = foo; bar.take() })(); false } => {},
   |                   ^^                 --- move occurs because `foo` has type `&mut Option<&i32>`, which does not implement the `Copy` trait
   |                   |
   |                   `foo` is moved here
   |
   = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
help: consider cloning the value if the performance cost is acceptable
   |
LL |             if { (|| { let mut bar = foo.clone(); bar.take() })(); false } => {},
   |                                         ++++++++
```

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/ui/span/send-is-not-static-ensures-scoping.stderr b/tests/ui/span/send-is-not-static-ensures-scoping.stderr
index bae0befcaca..c15547e8412 100644
--- a/tests/ui/span/send-is-not-static-ensures-scoping.stderr
+++ b/tests/ui/span/send-is-not-static-ensures-scoping.stderr
@@ -16,6 +16,9 @@ error[E0597]: `y` does not live long enough
    |
 LL |     let bad = {
    |         --- borrow later stored here
+LL |         let x = 1;
+LL |         let y = &x;
+   |             - binding `y` declared here
 ...
 LL |         scoped(|| {
    |                -- value captured here