Refactor TerminalTIState enum across Airflow components

### Description

- Move `TerminalTIState` enum from airflow.utils.state to right location
- Update all imports in airflow-core to use the new TerminalTIState location
- Add deprecation warning in airflow.utils.init.py for backward compatibility

### Use case/motivation

_No response_

### Related issues

https://github.com/apache/airflow/issues/53385
https://github.com/apache/airflow/issues/51671

### Are you willing to submit a PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start by reviewing related issues 53385 and 51671, then inspect TerminalTIState in airflow.utils.state and its imports across airflow-core. Determine the intended destination from the project structure, update the imports, and add the backward-compatibility deprecation warning in airflow.utils.init.py; done means the new location is used while the old import remains supported with a warning.

Written by the indexing model from the issue text.