Complex Dtype Support for Hashmap Algos
- [x] fixes #17927 #26475
- [x] tests added / passed
- [x] passes black pandas
- [x] passes git diff upstream/master -u -- "*.py" | flake8 --diff

Ref: https://github.com/pandas-dev/pandas/issues/18009

Based on https://github.com/pandas-dev/pandas/pull/27599

First set of tests for complex number handling + sensible results from functions that rely on hash tables.

Use generic object hashing for now.

@jbrockmendel you interested in reviewing?