TYPING: --check-untyped-defs for Index.__new__
xref #27568

```
pandas\core\indexes\base.py:335: error: Incompatible types in assignment (expression has type "TimedeltaIndex", variable has type "DatetimeIndex")
pandas\core\indexes\base.py:338: error: Incompatible types in assignment (expression has type "TimedeltaIndex", variable has type "DatetimeIndex")
pandas\core\indexes\base.py:346: error: Incompatible types in assignment (expression has type "PeriodIndex", variable has type "DatetimeIndex")
pandas\core\indexes\base.py:408: error: Name 'PeriodIndex' already defined on line 74
pandas\core\indexes\base.py:408: error: Module 'pandas.core.indexes.period' has no attribute 'IncompatibleFrequency'
pandas\core\indexes\base.py:419: error: Name 'Float64Index' already defined on line 349
pandas\core\indexes\base.py:443: error: Name 'Float64Index' already defined on line 349
pandas\core\indexes\base.py:447: error: Name 'IntervalIndex' already defined on line 170
pandas\core\indexes\base.py:459: error: Name 'DatetimeIndex' already defined on line 88
pandas\core\indexes\base.py:470: error: Name 'TimedeltaIndex' already defined on line 57
```

LGTM Thanks @simonjayhawkins 