feat: support chat format

[jhen0409]

Support convert OpenAI API compatible message ([{ role, content }, ...] and then llama_chat_apply_template.

• New field: context.model.isChatTemplateSupported
• context.completion(...): Add messages: RNLlamaOAICompatibleMessage[] in params
  • It is not recommended to use messages if the model is not supported chat template
• New util: context.getFormattedChat(messages: RNLlamaOAICompatibleMessage[]): string)
  • If the chat template is not supported in model, we will fallback to use chatml as format
  • context.completion also uses it to convert messages to prompt