* pymorph2 issues #11620, #11626, #11625:
- #11620: pymorphy2_lookup
- #11626: handle multiple forms pointing to the same normal form + handling empty POS tag
- #11625: matching DET that are labelled as PRON by pymorhp2
* Move lemmatizer algorithm changes back into RussianLemmatizer
* Fix uk pymorphy3_lookup mode init
* Move and update tests for ru/uk lookup lemmatizer modes
* Fix typo
* Remove traces of previous behavior for uninflected POS
* Refactor to private generic-looking pymorphy methods
* Remove xfailed uk lemmatizer cases
* Update spacy/lang/ru/lemmatizer.py
Co-authored-by: Richard Hudson <richard@explosion.ai>
Co-authored-by: Dmytro S Lituiev <d.lituiev@gmail.com>
Co-authored-by: Richard Hudson <richard@explosion.ai>
For the Russian and Ukrainian lemmatizers, restrict the `pymorphy2`
requirement to the mode `pymorphy2` so that lookup or other lemmatizer
modes can be loaded without installing `pymorphy2`.
