refactor SetHook preflight validation

include/xrpl/protocol/IOUAmount.h

@@ -97,6 +97,12 @@ class IOUAmount : private boost::totally_ordered<IOUAmount>,
 
     static IOUAmount
     minPositiveAmount();
+
+    friend std::ostream&
+    operator<<(std::ostream& os, IOUAmount const& x)
+    {
+        return os << to_string(x);
+    }
 };
 
 inline IOUAmount::IOUAmount(beast::Zero)

include/xrpl/protocol/Rules.h

@@ -28,6 +28,9 @@
 
 namespace ripple {
 
+bool
+isFeatureEnabled(uint256 const& feature);
+
 class DigestAwareReadView;
 
 /** Rules controlling protocol behavior. */

src/libxrpl/protocol/Rules.cpp

@@ -153,4 +153,12 @@ Rules::operator!=(Rules const& other) const
 {
     return !(*this == other);
 }
+
+bool
+isFeatureEnabled(uint256 const& feature)
+{
+    auto const& rules = getCurrentTransactionRules();
+    return rules && rules->enabled(feature);
+}
+
 }  // namespace ripple