Sort grammar map keys while pretty printing them

It would be too easy if we could just call sorted(). Thanks to zone
grammar the most important key "type" gets sorted near end, so we pull
it up to the top using a hack.

(cherry picked from commit 5c04e3c524)

doc/misc/checkgrammar.py

@@ -102,6 +102,14 @@ def diff_statements(whole_grammar, places):
 
 def pformat_grammar(node, level=1):
     """Pretty print a given grammar node in the same way as cfg_test would"""
+
+    def sortkey(item):
+        """Treat 'type' specially and always put it first, for zone types"""
+        key, _ = item
+        if key == "type":
+            return ""
+        return key
+
     if "_grammar" in node:  # no nesting
         assert "_id" not in node
         assert "_mapbody" not in node
@@ -118,7 +126,7 @@ def pformat_grammar(node, level=1):
             out += node["_id"] + " "
         out += "{\n"
 
-    for key, subnode in node["_mapbody"].items():
+    for key, subnode in sorted(node["_mapbody"].items(), key=sortkey):
         if not subnode.get("_ignore_this_level"):
             out += f"{indent}{subnode.get('_pprint_name', key)}"
             inner_grammar = pformat_grammar(node["_mapbody"][key], level=level + 1)