BUG: Fix joining overlapping IntervalIndex objects (GH-45661)
Replacing calls to `get_indexer()` with `get_indexer_for()` as
`IntervalIndex`es can be unique and overlapping.

Similar to #44588

- [x] closes #45661
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

thanks @johannes-mueller very nice @meeseeksdev backport 1.4.x Something went wrong ... Please have a look at my logs. @jbrockmendel this has been backported. The PR that is the cause of the regression was https://github.com/pandas-dev/pandas/pull/43692 which was some changes specifically targeted at IntervalIndex handling. The changes in this PR affect all Index types? (and the function changed is no longer appropriately named?) Can you give this a quick look and thumbs up before we release 1.4.1 (end of this week) This looks fine to me.