REF: merge_asof dont use values_for_argsort
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] 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
- [ ] whatsnew entry
cc @mroeschke @jreback 

Original motivation here was to remove an anti-pattern usage of _values_for_argsort.  In the process I found what I _think_ should be a bug, but I haven't been able to write a test that exposes it, could use some help.


Appears you're trying to tackle joining on nullables from which https://github.com/pandas-dev/pandas/issues/32306 would be relevant.  I think this should go in, as even if we don't have a test case that fails on the existing version, the version here i think is reliable.  Also this gets rid of the last clearly-antipattern usage of _values_for_argsort