[flang][NFC] Fix mis-matched struct/class declarations

[tskeith]

Summary

The template ListDirectedStatementState was declared as a struct and then as a class.
Fix it so they match.

[klausler]

The other specialization of this template is a class, though, so maybe the best fix is to change the earlier template struct to a class so that they all are so. I've got a fix on the way that does that, I think.

[tskeith]

In D88711#2307551, @klausler wrote:

The other specialization of this template is a class, though, so maybe the best fix is to change the earlier template struct to a class so that they all are so. I've got a fix on the way that does that, I think.

The only other specialization I see is immediately above and it's a struct.

[klausler]

In D88711#2307606, @tskeith wrote:

In D88711#2307551, @klausler wrote:

The other specialization of this template is a class, though, so maybe the best fix is to change the earlier template struct to a class so that they all are so. I've got a fix on the way that does that, I think.

The only other specialization I see is immediately above and it's a struct.

Ok. When I'm all done, it'll be a class, but I'll make sure to keep things consistent.

[tskeith]

Make them all class rather than struct.

flang/runtime/io-stmt.h

struct IoStatementBase : public DefaultFormatControlCallbacks {
   bool Inquire(InquiryKeywordHash, char *, std::size_t);
   bool Inquire(InquiryKeywordHash, bool &);
   bool Inquire(InquiryKeywordHash, std::int64_t, bool &);
   bool Inquire(InquiryKeywordHash, std::int64_t &);
   void BadInquiryKeywordHashCrash(InquiryKeywordHash);
 };
 
 // Common state for list-directed internal & external I/O
-template <Direction> struct ListDirectedStatementState;
+template <Direction> class ListDirectedStatementState;
 template <>
-struct ListDirectedStatementState<Direction::Output>
+class ListDirectedStatementState<Direction::Output>
     : public FormattedIoStatementState {
+public:
   static std::size_t RemainingSpaceInRecord(const ConnectionState &);
   bool NeedAdvance(const ConnectionState &, std::size_t) const;
   bool EmitLeadingSpaceOrAdvance(
       IoStatementState &, std::size_t, bool isCharacter = false);
   std::optional<DataEdit> GetNextDataEdit(
       IoStatementState &, int maxRepeat = 1);
   bool lastWasUndelimitedCharacter{false};
 };