Add `RoCBertTokenizer` to `TOKENIZER_MAPPING_NAMES`
# What does this PR do?

Add `RoCBertTokenizer` to `TOKENIZER_MAPPING_NAMES`.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20141). All of your documentation changes will be reflected on that endpoint.<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20141). All of your documentation changes will be reflected on that endpoint.