Add struct to doc hidden usefulness ui tests

src/test/ui/pattern/usefulness/auxiliary/hidden.rs

-pub enum Foo {
+pub enum HiddenEnum {
     A,
     B,
     #[doc(hidden)]
     C,
 }
+
+#[derive(Default)]
+pub struct HiddenStruct {
+    pub one: u8,
+    pub two: bool,
+    #[doc(hidden)]
+    pub hide: usize,
+}

src/test/ui/pattern/usefulness/doc-hidden-fields.rs

+// aux-build:hidden.rs
+
+extern crate hidden;
+
+use hidden::HiddenStruct;
+
+fn main() {
+    let HiddenStruct { one, two, } = HiddenStruct::default();
+    //~^ pattern requires `..` due to inaccessible fields
+
+    let HiddenStruct { one, } = HiddenStruct::default();
+    //~^ pattern does not mention field `two` and inaccessible fields
+
+    let HiddenStruct { one, hide } = HiddenStruct::default();
+    //~^ pattern does not mention field `two`
+}

src/test/ui/pattern/usefulness/doc-hidden-non-exhaustive.rs

@@ -2,29 +2,29 @@
 
 extern crate hidden;
 
-use hidden::Foo;
+use hidden::HiddenEnum;
 
 fn main() {
-    match Foo::A {
-        Foo::A => {}
-        Foo::B => {}
+    match HiddenEnum::A {
+        HiddenEnum::A => {}
+        HiddenEnum::B => {}
     }
     //~^^^^ non-exhaustive patterns: `_` not covered
 
-    match Foo::A {
-        Foo::A => {}
-        Foo::C => {}
+    match HiddenEnum::A {
+        HiddenEnum::A => {}
+        HiddenEnum::C => {}
     }
     //~^^^^ non-exhaustive patterns: `B` not covered
 
-    match Foo::A {
-        Foo::A => {}
+    match HiddenEnum::A {
+        HiddenEnum::A => {}
     }
     //~^^^ non-exhaustive patterns: `B` and `_` not covered
 
     match None {
         None => {}
-        Some(Foo::A) => {}
+        Some(HiddenEnum::A) => {}
     }
     //~^^^^ non-exhaustive patterns: `Some(B)` and `Some(_)` not covered
 }