BUG: get_loc / get_indexer with NaT and tz-aware DatetimeIndex
#### Code Sample, a copy-pastable example if possible

```python
>>> pd.date_range('2020', 'now').get_loc(pd.NaT, method='nearest')
0
    # Ok? NaT would be better to propagate.

>>> pd.date_range('2020', 'now', tz='US/Central').get_loc(pd.NaT, method='nearest')
-----------------------------------------------------------------------------------
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "pandas/core/indexes/datetimes.py", line 582, in get_loc
    return Index.get_loc(self, key, method, tolerance)
  File "pandas/core/indexes/base.py", line 2869, in get_loc
    indexer = self.get_indexer([key], method=method, tolerance=tolerance)
  File "pandas/core/indexes/base.py", line 2951, in get_indexer
    target, method=method, limit=limit, tolerance=tolerance
  File "pandas/core/indexes/base.py", line 2962, in get_indexer
    indexer = self._get_nearest_indexer(target, limit, tolerance)
  File "pandas/core/indexes/base.py", line 3046, in _get_nearest_indexer
    left_distances = np.abs(self[left_indexer] - target)
  File "pandas/core/indexes/base.py", line 2361, in __sub__
    return Index(np.array(self) - other)
  File "pandas/core/indexes/base.py", line 2367, in __rsub__
    return Index(other - Series(self))
  File "pandas/core/series.py", line 646, in __array_ufunc__
    self, ufunc, method, *inputs, **kwargs
  File "pandas/_libs/ops_dispatch.pyx", line 91, in pandas._libs.ops_dispatch.maybe_dispatch_ufunc_to_dunder_op
  File "pandas/core/ops/common.py", line 63, in new_method
    return method(self, other)
  File "pandas/core/ops/__init__.py", line 500, in wrapper
    result = arithmetic_op(lvalues, rvalues, op, str_rep)
  File "pandas/core/ops/array_ops.py", line 218, in arithmetic_op
    res_values = dispatch_to_extension_op(op, lvalues, rvalues)
  File "pandas/core/ops/dispatch.py", line 125, in dispatch_to_extension_op
    res_values = op(left, right)
  File "pandas/core/ops/roperator.py", line 13, in rsub
    return right - left
  File "pandas/core/arrays/datetimelike.py", line 1428, in __rsub__
    f"cannot subtract {type(self).__name__} from {type(other).__name__}"
TypeError: cannot subtract DatetimeArray from ndarray
```
#### Problem description

`pd.NaT` is NaT regardless of timezone.

#### Expected Output

```py

>>> pd.date_range('2020', 'now').get_loc(pd.NaT, method='nearest')
NaT

>>> pd.date_range('2020', 'now', tz='US/Central').get_loc(pd.NaT, method='nearest')
NaT
```

#### Output of ``pd.show_versions()``

<details>

pandas 1.1.0.dev0+725.gae79bb23c

</details>
