[ruby/prism] Add keyword_loc to ForwardingSuperNode

They can take a block and so the keyword location is not always the entirety of the node.
You can get it by constructing a location that is just the first 5 characters
but why not have it be provided by prism?

ruby/prism@878d79eb8c

Author: Earlopain

prism/config.yml

@@ -2627,6 +2627,14 @@ nodes:
           end
   - name: ForwardingSuperNode
     fields:
+      - name: keyword_loc
+        type: location
+        comment: |
+          super
+          ^^^^^
+
+          super { 123 }
+          ^^^^^
       - name: block
         type: node?
         kind: BlockNode

prism/prism.c

@@ -4379,6 +4379,7 @@ pm_forwarding_super_node_create(pm_parser_t *parser, const pm_token_t *token, pm
         ++parser->node_id,
         0,
         (block == NULL) ? PM_LOCATION_INIT_TOKEN(parser, token) : PM_LOCATION_INIT_TOKEN_NODE(parser, token, block),
+        PM_LOCATION_INIT_TOKEN(parser, token),
         block
     );
 }