Fix SS03 Issues in Docstrings

Running the following: scripts/validate_docstrings.py --errors=SS03 returns the following instances of cases where the Summary doesn’t end with a period. SS03 is one of the pending docstring-related errors as mentioned in #27977

• pandas.tseries.frequencies.to_offset: Summary does not end with a period
• pandas.Int64Index: Summary does not end with a period
• pandas.UInt64Index: Summary does not end with a period
• pandas.Float64Index: Summary does not end with a period
• pandas.IntervalIndex.left: Summary does not end with a period
• pandas.IntervalIndex.right: Summary does not end with a period
• pandas.IntervalIndex.mid: Summary does not end with a period
• pandas.IntervalIndex.closed: Summary does not end with a period
• pandas.IntervalIndex.length: Summary does not end with a period
• pandas.io.stata.StataReader.data: Summary does not end with a period
• pandas.plotting.plot_params: Summary does not end with a period
• pandas.io.formats.style.Styler.loader: Summary does not end with a period
• pandas.Timestamp.combine: Summary does not end with a period
• pandas.Timestamp.fromordinal: Summary does not end with a period
• pandas.Timestamp.isoweekday: Summary does not end with a period
• pandas.Timestamp.weekday: Summary does not end with a period
• pandas.Period.strftime: Summary does not end with a period
• pandas.Interval.closed: Summary does not end with a period
• pandas.Interval.left: Summary does not end with a period
• pandas.Interval.length: Summary does not end with a period
• pandas.Interval.mid: Summary does not end with a period
• pandas.Interval.right: Summary does not end with a period

The way to go about resolving this issue with such a large number of files has been nicely setup by @datapythonista in #27977 itself. Quoting from the issue:

> VERY IMPORTANT The main challenge will be not repeating the same work as other sprinters, which is very frustrating, and happened massively at every sprint. My recommendation is BEFORE doing any work, to create an issue for the error code you plan to work on (check that it hasn’t already been created). In the error write the list of errors that validate_docstrings.py returns. Then in a comment, take 10 of them, and write that you’re going to fix them. Other people can work on a different 10. When opening a PR, reference the issue.

[UPDATE 1] List has been updated after @datapythonista’s recommendation to remove the ones starting with pandas.tseries.offsets .

[datapythonista]

When changing .pyx files, you need to recompile pandas with python setup.py build_ext --inplace -j 0 for the script to see the changes. If that’s not the problem, please send me a link to of the docstring you’re changing, and the output of the script, and I’ll have a look.

[datapythonista]

Afaik all the ones starting with pandas.tseries.offsets are false positives, we’re working on fixing the script so they are not mistakenly reported.