PERF: StringArray from np.str_ array
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added an entry in the latest `doc/source/whatsnew/v2.0.0.rst` file if fixing a bug or adding a new feature.

Perf improvement when constructing a `StringArray` from a numpy array with type `np.str_`. 

```
       before           after         ratio
     [fb19ddbf]       [a4b0d732]
     <main>           <string-array-np-str>
-      23.0±0.8ms      6.15±0.04ms     0.27  array.StringArray.time_from_np_str_array
- ```
Thanks @lukemanley 