POC: DataFrame.stack not including NA rows
Demonstration for #53515

- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

@jorisvandenbossche - there are some cases where DataFrame.stack sorts the result; I believe these are bugs. Other than this, the only tricky situation I've encountered is handling duplicates in the column that is being stacked. In this POC, I raise a ValueError instead. See #53761  Closing in favor of #53921. @jorisvandenbossche - happy to continue any discussion here, or move over to #53921.