Tweak spans when encountering multiline initializer in move error

```
error[E0507]: cannot move out of `f`, a captured variable in an `FnMut` closure
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:57:13
   |
LL |     let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| {
   |         ----- captured outer variable
...
LL |     f(Box::new(|a| {
   |                --- captured by this `FnMut` closure
LL |
LL |         foo(f);
   |             ^ move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait
```

instead of

```
error[E0507]: cannot move out of `f`, a captured variable in an `FnMut` closure
  --> $DIR/borrowck-call-is-borrow-issue-12224.rs:57:13
   |
LL |       let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| {
   |  _________-----___-
   | |         |
   | |         captured outer variable
LL | |         let _ = s.len();
LL | |     };
   | |_____- move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait
LL |       f(Box::new(|a| {
   |                  --- captured by this `FnMut` closure
LL |
LL |           foo(f);
   |               ^ `f` is moved here
```

Author: estebank

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -663,8 +663,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                             //    |        |         `Option<Foo>`, which does not implement the
                             //    |        |         `Copy` trait
                             //    |        captured outer variable
-                            (None, Some(init)) => init.span,
-                            (None, None) => use_span,
+                            //
+                            // We don't want the case where the initializer is something that spans
+                            // multiple lines, like a closure, as the ASCII art gets messy.
+                            (None, Some(init))
+                                if !self.infcx.tcx.sess.source_map().is_multiline(init.span) =>
+                            {
+                                init.span
+                            }
+                            _ => use_span,
                         },
                         _ => use_span,
                     };

tests/ui/borrowck/unboxed-closures-move-upvar-from-non-once-ref-closure.stderr

@@ -2,15 +2,13 @@ error[E0507]: cannot move out of `y`, a captured variable in an `Fn` closure
   --> $DIR/unboxed-closures-move-upvar-from-non-once-ref-closure.rs:12:9
    |
 LL |     let y = vec![format!("World")];
-   |         -   ---------------------- move occurs because `y` has type `Vec<String>`, which does not implement the `Copy` trait
-   |         |
-   |         captured outer variable
+   |         - captured outer variable
 LL |     call(|| {
    |          -- captured by this `Fn` closure
 LL |         y.into_iter();
    |         ^ ----------- `y` moved due to this method call
    |         |
-   |         `y` is moved here
+   |         move occurs because `y` has type `Vec<String>`, which does not implement the `Copy` trait
    |
 note: `into_iter` takes ownership of the receiver `self`, which moves `y`
   --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL

tests/ui/span/borrowck-call-is-borrow-issue-12224.stderr

@@ -35,18 +35,14 @@ LL | fn test4(f: &mut Test) {
 error[E0507]: cannot move out of `f`, a captured variable in an `FnMut` closure
   --> $DIR/borrowck-call-is-borrow-issue-12224.rs:57:13
    |
-LL |       let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| {
-   |  _________-----___-
-   | |         |
-   | |         captured outer variable
-LL | |         let _ = s.len();
-LL | |     };
-   | |_____- move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait
-LL |       f(Box::new(|a| {
-   |                  --- captured by this `FnMut` closure
+LL |     let mut f = move |g: Box<dyn FnMut(isize)>, b: isize| {
+   |         ----- captured outer variable
+...
+LL |     f(Box::new(|a| {
+   |                --- captured by this `FnMut` closure
 LL |
-LL |           foo(f);
-   |               ^ `f` is moved here
+LL |         foo(f);
+   |             ^ move occurs because `f` has type `{closure@$DIR/borrowck-call-is-borrow-issue-12224.rs:52:17: 52:58}`, which does not implement the `Copy` trait
    |
 help: consider cloning the value if the performance cost is acceptable
    |