refactor: Split util::insert into its own file

src/util/insert.h

@@ -0,0 +1,24 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_INSERT_H
+#define BITCOIN_UTIL_INSERT_H
+
+#include <set>
+
+namespace util {
+
+//! Simplification of std insertion
+template <typename Tdst, typename Tsrc>
+inline void insert(Tdst& dst, const Tsrc& src) {
+    dst.insert(dst.begin(), src.begin(), src.end());
+}
+template <typename TsetT, typename Tsrc>
+inline void insert(std::set<TsetT>& dst, const Tsrc& src) {
+    dst.insert(src.begin(), src.end());
+}
+
+} // namespace util
+
+#endif // BITCOIN_UTIL_INSERT_H