PERF: constructing string Series

[topper-123]

Avoid needless call to lib.infer_dtype, when string dtype.

Performance example:

>>> x = np.array([str(u) for u in range(1_000_000)], dtype=object)
>>> %timeit pd.Series(x, dtype=str)
344 ms ± 59.7 ms per loop  # v1.1.0
157 ms ± 7.04 ms per loop  # after #35519
22.6 ms ± 191 µs per loop  # after #36304
11.2 ms ± 48.6 µs per loop  # after this PR

Similar speed-up is possible for pd.Series(x, dtype="string"), but requires some refactorng of StringArray, so I'll do that is a seperate PR.

xref #35519 & #36304.

[jreback]

great (can u add all of these issues on the whats new, same entry just keep appending)

[topper-123]

Updated.

[jreback]

thanks @topper-123