PERF: Datetime/Timestamp.normalize for timezone naive datetimes
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

```
       before           after         ratio
     [bb32564c]       [ff171f75]
-         281±2μs          197±2μs     0.70  timeseries.DatetimeIndex.time_normalize('dst')
-     4.26±0.05ms      2.64±0.04ms     0.62  timeseries.DatetimeAccessor.time_dt_accessor_normalize
-     3.78±0.01ms      2.28±0.01ms     0.60  timeseries.DatetimeIndex.time_normalize('repeated')
-     3.79±0.05ms      2.23±0.06ms     0.59  timeseries.DatetimeIndex.time_normalize('tz_naive')


       before           after         ratio
     [bb32564c]       [ff171f75]
-      11.9±0.9μs         1.56±0μs     0.13  timestamp.TimestampOps.time_normalize(None)
```