DEV: coccinelle: Add rule to use `chunk_istcat()` instead of `chunk_memcat()`

This replaces `chunk_memcat()` with `chunk_istcat()` if the parameters are the
ist's `.ptr` and `.len`.

dev/coccinelle/ist.cocci

@@ -52,6 +52,14 @@ expression e;
 - if (\(i.len\|istlen(i)\) > e) { i.len = e; }
 + i = isttrim(i, e);
 
+@@
+struct ist i;
+struct buffer *b;
+@@
+
+- chunk_memcat(b, \(i.ptr\|istptr(i)\) , \(i.len\|istlen(i)\));
++ chunk_istcat(b, i);
+
 @@
 struct ist i;
 @@