pallet-macro: Ensure that building with missing_docs works (#11075)

* pallet-macro: Ensure that building with `missing_docs` works

Before this pr it was failing when compiling with `missing_docs`, because the macro was generating
functions etc without the appropriate docs. In the case of this pr it is mainly about hiding these
functions in the docs as they are internal api anyway.

* Fix UI test

substrate/frame/support/test/pallet/src/lib.rs

@@ -14,6 +14,12 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+//! Testing pallet macro
+
+// Ensure docs are propagated properly by the macros.
+#![warn(missing_docs)]
+
 pub use pallet::*;
 
 #[frame_support::pallet]
@@ -29,6 +35,10 @@ pub mod pallet {
 	#[pallet::config]
 	pub trait Config: frame_system::Config {}
 
+	/// I'm the documentation
+	#[pallet::storage]
+	pub type Value<T> = StorageValue<Value = u32>;
+
 	#[pallet::genesis_config]
 	#[cfg_attr(feature = "std", derive(Default))]
 	pub struct GenesisConfig {}
@@ -37,4 +47,10 @@ pub mod pallet {
 	impl<T: Config> GenesisBuild<T> for GenesisConfig {
 		fn build(&self) {}
 	}
+
+	#[pallet::error]
+	pub enum Error<T> {
+		/// Something failed
+		Test,
+	}
 }