MCore dataset compatibility for tokenizers
@ericharper / @dimapihtar can you review this fix?  Thanks! jenkins jenkins jenkins jenkins jenkins jenkins jenkins
# What does this PR do ?

Adds properties required by megatron-core to NeMo tokenizers via the base TokenizerSpec class (see #8283).

**Collection**: common (tokenizers)

# Changelog 
- Adds a `unique_identifiers` OrderedDict which is needed when using alongside megatron-core datasets (following [megatron_tokenizer.py](https://github.com/NVIDIA/Megatron-LM/blob/0052bf0de70b266d8648e2655da16f7eb2c9ca56/megatron/core/datasets/megatron_tokenizer.py))
- Adds several property-decorated methods as aliases for equivalent properties already present in tokenizers that inherit from TokenizerSpec
- Removes now-redundant individual fix from AutoTokenizer

# Usage
* You can potentially add a usage example below

```python
# Add a code snippet demonstrating how to use this 
```

# Jenkins CI
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**PR Type**:
- [ ] New Feature
- [ ] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
