Change preprocessor options for string_view to be more consistent with other options

Also makes it so people can manually define MODERN_SQLITE_STRINGVIEW_SUPPORT if they want

Author: jimmyjxiao

hdr/sqlite_modern_cpp/type_wrapper.h

@@ -7,16 +7,7 @@
 #ifdef __has_include
 #if __cplusplus >= 201703 && __has_include(<string_view>)
 #define MODERN_SQLITE_STRINGVIEW_SUPPORT
-#include <string_view>
-#define STR_REF std::string_view
-#define U16STR_REF std::u16string_view
-#else
-#define STR_REF std::string
-#define U16STR_REF std::u16string
 #endif
-#else
-#define STR_REF std::string
-#define U16STR_REF std::u16string
 #endif
 #ifdef __has_include
 #if __cplusplus > 201402 && __has_include(<optional>)
@@ -44,7 +35,14 @@
 #ifdef MODERN_SQLITE_STD_VARIANT_SUPPORT
 #include <variant>
 #endif
-
+#ifdef MODERN_SQLITE_STRINGVIEW_SUPPORT
+#include <string_view>
+#define STR_REF std::string_view
+#define U16STR_REF std::u16string_view
+#else
+#define STR_REF std::string
+#define U16STR_REF std::u16string
+#endif
 #include <sqlite3.h>
 #include "errors.h"