Move EnumString to separate file and add enum_to_string (#15714)

src/util/enum_string.cpp

@@ -0,0 +1,31 @@
+// Luanti
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// Copyright (C) 2025 cx384
+
+#include "util/enum_string.h"
+#include <cassert>
+
+bool string_to_enum(const EnumString *spec, int &result, std::string_view str)
+{
+	const EnumString *esp = spec;
+	while (esp->str) {
+		if (str == esp->str) {
+			assert(esp->num >= 0);
+			result = esp->num;
+			return true;
+		}
+		esp++;
+	}
+	return false;
+}
+
+const char *enum_to_string(const EnumString *spec, int num)
+{
+	if (num < 0)
+		return nullptr;
+	// assume array order matches enum order
+	auto *p = &spec[num];
+	assert(p->num == num);
+	assert(p->str);
+	return p->str;
+}