Improve the readability of STBase-derived types

* Increase the visibility of each type's API.
* No functional changes.

src/ripple/protocol/impl/STValidation.cpp

@@ -25,6 +25,18 @@
 
 namespace ripple {
 
+STBase*
+STValidation::copy(std::size_t n, void* buf) const
+{
+    return emplace(n, buf, *this);
+}
+
+STBase*
+STValidation::move(std::size_t n, void* buf)
+{
+    return emplace(n, buf, std::move(*this));
+}
+
 SOTemplate const&
 STValidation::validationFormat()
 {