TST: Use fixtures instead of setup_method for index tests
The common index tests use `setup_method` to create a `dict` of indexes to test against:

https://github.com/pandas-dev/pandas/blob/df2e0813e053cc5bc924b2292ea8918a6b27f0e2/pandas/tests/indexes/test_range.py#L25-L30

This `dict` of indexes is then iterated over within the tests:

https://github.com/pandas-dev/pandas/blob/df2e0813e053cc5bc924b2292ea8918a6b27f0e2/pandas/tests/indexes/common.py#L359-L363

The bulk of this PR involves converting `self.indices` into a parametrized fixture of indexes, and adjusting the tests to support this (largely just unindenting).  I had to do this conversion for all indexes at once since common test code for all index classes utilizes this pattern, so the diff is fairly large, but it should be relatively simple changes.

I also had to make some changes to references to specific indexes as well (e.g. `self.index`, `self.strIndex`, etc.) since the `setup_method` code also directly set each index in the `dict` as a class attribute.