Fix multiline docstring quote normalization

The quotes of multiline docstrings are now only normalized when string
normalization is off, instead of the string normalization setting being
ignored and the quotes being *always* normalized.

I had to make a new test case and data file since the current pair for
docstrings only worked when there is no formatting difference between the
formatting results with string normalization on and off. I needed to add
tests for when there *are* differences between the two. So I split
test_docstring's test code when string normalization is disabled into a
new test case along with a new data file.