Suggest struct pat on incorrect unit or tuple pat

When encountering a unit or tuple pattern for a struct-like item, suggest
using the correct pattern.

Use `insert_field_names_local` when evaluating variants and store field
names even when the list is empty in order to produce accurate
structured suggestions.

src/test/ui/error-codes/E0423.stderr

@@ -33,13 +33,16 @@ LL |     struct Foo { a: bool };
    |     ---------------------- `Foo` defined here
 LL | 
 LL |     let f = Foo();
+   |             ^^^^^
+   |
+help: a function with a similar name exists
+   |
+LL |     let f = foo();
    |             ^^^
-   |             |
-   |             did you mean `Foo { /* fields */ }`?
-   |             help: a function with a similar name exists (notice the capitalization): `foo`
-...
-LL | fn foo() {
-   | -------- similarly named function `foo` defined here
+help: use struct literal syntax instead
+   |
+LL |     let f = Foo { a: val };
+   |             ^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found struct `T`
   --> $DIR/E0423.rs:14:8