Add support for internally tagged enums in non self-describing formats

Deserializer methods are only hints which deserializer is not obliged to follow.
Both TaggedContentVisitor and InternallyTaggedUnitVisitor accepts only
visit_map and visit_seq and that is what derived implementation of Deserialize
does for structs. Therefore it is fine to call deserialize_map here, as that
already did in derived deserialize implementation

serde_derive/src/de.rs

@@ -1392,7 +1392,7 @@ fn deserialize_internally_tagged_enum(
 
         #variants_stmt
 
-        let (__tag, __content) = _serde::Deserializer::deserialize_any(
+        let (__tag, __content) = _serde::Deserializer::deserialize_map(
             __deserializer,
             _serde::__private::de::TaggedContentVisitor::<__Field>::new(#tag, #expecting))?;
         let __deserializer = _serde::__private::de::ContentDeserializer::<__D::Error>::new(__content);
@@ -1840,7 +1840,7 @@ fn deserialize_internally_tagged_variant(
                 quote!((#default))
             });
             quote_block! {
-                _serde::Deserializer::deserialize_any(#deserializer, _serde::__private::de::InternallyTaggedUnitVisitor::new(#type_name, #variant_name))?;
+                _serde::Deserializer::deserialize_map(#deserializer, _serde::__private::de::InternallyTaggedUnitVisitor::new(#type_name, #variant_name))?;
                 _serde::__private::Ok(#this_value::#variant_ident #default)
             }
         }