API: Index(object_dtype_bool_ndarray) retain object dtype

[jbrockmendel]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[mroeschke]

Just to solidify the "rule of thumb" where this is headed

pd.Index/Series(np.array([...], dtype=object), dtype=None) -> object
pd.Index/Series(np.array([...], dtype=object), dtype=other) == pd.Index/Series(np.array([...], dtype=object)).astype(other)

?

[mroeschke]

Thanks @jbrockmendel

[jbrockmendel]

Just to solidify the "rule of thumb" where this is headed [...]

Not quite. In the pd.Index/Series(ndarray_object) case we'll continue to do inference on datetime, timedelta, interval, and period.

(and more generally id have no strong objection to doing inference on numeric/bool dtypes, just as long as we're consistent about it)