When a struct definition has default field values, and the use struct ctor has missing field, if all those missing fields have defaults suggest `..`:
```
error[E0063]: missing fields `field1` and `field2` in initializer of `S`
--> $DIR/non-exhaustive-ctor.rs:16:13
|
LL | let _ = S { field: () };
| ^ missing `field1` and `field2`
|
help: all remaining fields have defaults, use `..`
|
LL | let _ = S { field: (), .. };
| ++++
```
