Move some general code generation helpers into their own file

src/compiler/generate_code/helpers.h

@@ -0,0 +1,19 @@
+#ifndef __tree_sitter__helpers__
+#define __tree_sitter__helpers__
+
+#include <string>
+#include <vector>
+
+namespace tree_sitter {
+    using std::string;
+    using std::vector;
+
+    namespace generate_code {
+        string indent(string input);
+        string join(vector<string> lines, string separator);
+        string join(vector<string> lines);
+        string escape_string(string input);
+    }
+}
+
+#endif