Feature Request: Cache invalidation methods

[apackin]

Currently to invalidate a cached query I'm doing:

   invalidateCachedQuery(queryDocument) {
    final cacheQueries = _store.get('Query');
    if (cacheQueries == null) return;
    final cachedNodeDefinition = queryDocument.definitions.whereType().first;
    final topLevelSelectionSet = cachedNodeDefinition?.selectionSet?.selections;
    topLevelSelectionSet.forEach((selection) {
      final cacheKey = selection.name.value;
      if (cacheKey != '__typename' && cacheQueries.containsKey(cacheKey)) {
        cacheQueries.remove(cacheKey);
      }
    });
  }
  
  invalidateCachedQuery$GetState() {
    invalidateCachedQuery(documentNodeQueryGetState);
  }

It would be great if there was a shorthand like client.invalidateQuery$GetState() that handled this for all queries.

[apackin]

I updated the example code based on #173, looks like they're trying to accomplish a similar goal of flagging cached queries as invalid.