use type name in E0599 enum variant suggestion

Also, rename the variable from "type_str" to "item_kind" to avoid
the ambiguity that caused this bug.

src/test/ui/issue-23217.stderr

@@ -6,7 +6,7 @@ LL | pub enum SomeEnum {
 LL |     B = SomeEnum::A,
    |         ^^^^^^^^^^^ variant not found in `SomeEnum`
    |
-   = note: did you mean `variant::B`?
+   = note: did you mean `SomeEnum::B`?
 
 error: aborting due to previous error
 

src/test/ui/issue-28971.stderr

@@ -7,7 +7,7 @@ LL | enum Foo {
 LL |             Foo::Baz(..) => (),
    |             ^^^^^^^^^^^^ variant not found in `Foo`
    |
-   = note: did you mean `variant::Bar`?
+   = note: did you mean `Foo::Bar`?
 
 error: aborting due to previous error