Remove the separator characters construct

Now, grammars can handle whitespace by making it another ubiquitous
token, like comments.

For now, this has the side effect of whitespace being included in the
tree that precedes it. This was already an issue for other ubiquitous
tokens though, so it needs to be fixed anyway.

src/runtime/stack.c

@@ -50,7 +50,26 @@ size_t ts_stack_right_position(const TSStack *stack) {
   size_t result = 0;
   for (size_t i = 0; i < stack->size; i++) {
     TSTree *node = stack->entries[i].node;
-    result += ts_tree_total_size(node);
+    result += node->size;
   }
   return result;
 }
+
+TSTree **ts_stack_pop_extras(TSStack *stack, size_t *count) {
+  size_t first = stack->size;
+  while (first > 0 && ts_tree_is_extra(stack->entries[first - 1].node))
+    first--;
+
+  *count = (stack->size - first);
+  if (*count == 0)
+    return NULL;
+
+  TSTree **result = malloc(*count * sizeof(TSTree *));
+  for (size_t i = 0; i < *count; i++) {
+    result[i] = stack->entries[first + i].node;
+    ts_tree_retain(result[i]);
+  }
+
+  ts_stack_shrink(stack, first - 1);
+  return result;
+}