[WIP] Windows CI

Based on !186 (closed) . Example of successful run: https://gitlab.com/elsid/openmw/-/jobs/544966421. The main problem with out of memory errors is solved by reducing max number of parallel processes to 1. Only engine itself can be using gitlab pipeline here within 1 hour. Adding editor makes build time about 58-60 mins. Timeout happens on cache saving. I've tried to play with /Zm flag following microsoft guide. Build with /Zm10 still crashes. And I didn't find any other good advices.