BUG: cannot construct Index of empty tuples

[batterseapower]

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Reproducible Example

import pandas as pd
pd.Index([()]) # Fails, the MultiIndex constructor complains that you "must pass non-zero number of levels/codes"
pd.Index([(), None])[:1] # Works

Issue Description

The index constructor has a special case for when the input list consists purely of tuples. However, it's not aware of the special case in MultiIndex that forbids number of levels == 0. Index should avoid trying to construct a MultiIndex in this case.

(Even better, MultiIndex could just support 0-level indexes. Yes, they are trivial in some sense, but they are also perfectly sensible.)

Expected Behavior

Both lines should evaluate correctly to identical indexes.

Installed Versions

INSTALLED VERSIONS ------------------ commit : 945c9ed python : 3.8.12.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19042 machine : AMD64 processor : Intel64 Family 6 Model 85 Stepping 7, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : English_United Kingdom.1252

pandas : 1.3.4
numpy : 1.21.3
pytz : 2021.3
dateutil : 2.8.2
pip : 21.1.1
setuptools : 58.0.4
Cython : 0.29.24
pytest : 6.2.4
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.6.3
html5lib : 1.1
pymysql : None
psycopg2 : None
jinja2 : 3.0.2
IPython : 7.29.0
pandas_datareader: None
bs4 : 4.10.0
bottleneck : 1.3.2
fsspec : 2021.08.1
fastparquet : None
gcsfs : None
matplotlib : 3.4.3
numexpr : 2.7.3
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : 3.0.0
pyxlsb : None
s3fs : None
scipy : 1.6.2
sqlalchemy : None
tables : 3.6.1
tabulate : None
xarray : 0.19.0
xlrd : 2.0.1
xlwt : None
numba : 0.53.1