collect index formatting tests

It looks like PeriodIndex/TDI/DTI tests are using different rules for what constitutes test_indexing/test_setops.  Double-checking before making a PR:

test_get_loc_* --> test_indexing
test_get_indexer_* --> test_indexing
test_insert_* --> test_indexing
test_where_* --> test_indexing
test_join_* --> test_setops
test_append_* --> test_setops
test_difference_* --> test_setops

Many of these at the moment are in e.g. test_ops or test_period/test_datetime.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=h1) Report
> Merging [#19661](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2fdf1e256e5e0b7f1fe909629e2f0b7893c8c7c3?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19661/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #19661   +/-   ##
=======================================
  Coverage   91.58%   91.58%           
=======================================
  Files         150      150           
  Lines       48867    48867           
=======================================
  Hits        44755    44755           
  Misses       4112     4112
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.96% <ø> (ø)` | :arrow_up: |
| #single | `41.75% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=footer). Last update [2fdf1e2...a5c00d1](https://codecov.io/gh/pandas-dev/pandas/pull/19661?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!