Recognize type Alias = dyn Trait in fn return types

```
error[E0277]: the size for values of type `(dyn Debug + 'static)` cannot be known at compilation time
  --> $DIR/dyn-trait-type-alias-return-type.rs:4:11
   |
LL | fn f() -> T { loop {} }
   |           ^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `(dyn Debug + 'static)`
note: this type alias is unsized
  --> $DIR/dyn-trait-type-alias-return-type.rs:1:1
   |
LL | type T = dyn core::fmt::Debug;
   | ^^^^^^
   = note: the return type of a function must have a statically known size
```

Author: estebank

tests/ui/future_not_send.stderr

@@ -1,8 +1,8 @@
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:8:1
+  --> tests/ui/future_not_send.rs:8:62
    |
 LL | async fn private_future(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `private_future` is not `Send`
+   |                                                              ^^^^ future returned by `private_future` is not `Send`
    |
 note: future is not `Send` as this value is used across an await
   --> tests/ui/future_not_send.rs:11:20
@@ -23,10 +23,10 @@ LL | async fn private_future(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
    = help: to override `-D warnings` add `#[allow(clippy::future_not_send)]`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:14:1
+  --> tests/ui/future_not_send.rs:14:41
    |
 LL | pub async fn public_future(rc: Rc<[u8]>) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `public_future` is not `Send`
+   |                                         ^ future returned by `public_future` is not `Send`
    |
 note: future is not `Send` as this value is used across an await
   --> tests/ui/future_not_send.rs:17:20
@@ -39,10 +39,10 @@ LL |     async { true }.await;
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Send`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:24:1
+  --> tests/ui/future_not_send.rs:24:63
    |
 LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `private_future2` is not `Send`
+   |                                                               ^^^^ future returned by `private_future2` is not `Send`
    |
 note: captured value is not `Send`
   --> tests/ui/future_not_send.rs:24:26
@@ -58,10 +58,10 @@ LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
    = note: `std::cell::Cell<usize>` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:30:1
+  --> tests/ui/future_not_send.rs:30:42
    |
 LL | pub async fn public_future2(rc: Rc<[u8]>) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `public_future2` is not `Send`
+   |                                          ^ future returned by `public_future2` is not `Send`
    |
 note: captured value is not `Send`
   --> tests/ui/future_not_send.rs:30:29
@@ -71,10 +71,10 @@ LL | pub async fn public_future2(rc: Rc<[u8]>) {}
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Send`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:42:5
+  --> tests/ui/future_not_send.rs:42:39
    |
 LL |     async fn private_future(&self) -> usize {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `private_future` is not `Send`
+   |                                       ^^^^^ future returned by `private_future` is not `Send`
    |
 note: future is not `Send` as this value is used across an await
   --> tests/ui/future_not_send.rs:45:24
@@ -87,10 +87,10 @@ LL |         async { true }.await;
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:49:5
+  --> tests/ui/future_not_send.rs:49:38
    |
 LL |     pub async fn public_future(&self) {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `public_future` is not `Send`
+   |                                      ^ future returned by `public_future` is not `Send`
    |
 note: captured value is not `Send` because `&` references cannot be sent unless their referent is `Sync`
   --> tests/ui/future_not_send.rs:49:32
@@ -100,13 +100,10 @@ LL |     pub async fn public_future(&self) {
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:61:1
+  --> tests/ui/future_not_send.rs:61:37
    |
-LL | / async fn generic_future<T>(t: T) -> T
-LL | |
-LL | | where
-LL | |     T: Send,
-   | |____________^ future returned by `generic_future` is not `Send`
+LL | async fn generic_future<T>(t: T) -> T
+   |                                     ^ future returned by `generic_future` is not `Send`
    |
 note: future is not `Send` as this value is used across an await
   --> tests/ui/future_not_send.rs:67:20
@@ -118,10 +115,10 @@ LL |     async { true }.await;
    = note: `T` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely
-  --> tests/ui/future_not_send.rs:83:1
+  --> tests/ui/future_not_send.rs:83:51
    |
 LL | async fn generic_future_always_unsend<T>(_: Rc<T>) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `generic_future_always_unsend` is not `Send`
+   |                                                   ^ future returned by `generic_future_always_unsend` is not `Send`
    |
 note: future is not `Send` as this value is used across an await
   --> tests/ui/future_not_send.rs:86:20