Use C++ user-defined literals for creating YulString constants.

libyul/YulString.h

@@ -127,4 +127,9 @@ private:
 	YulStringRepository::Handle m_handle{ 0, YulStringRepository::emptyHash() };
 };
 
+inline YulString operator "" _yulstring(const char *_string, std::size_t _size)
+{
+	return YulString(std::string(_string, _size));
+}
+
 }