use Android API directly for GPS location instead of relying on proprietary Google Services

[violoncelloCH]

I just have a concern regarding the use of the proprietary google play library. Since we so far managed to avoid dependencies on any proprietary library, this makes the app require the presence of Googles proprietary services. It will not work on devices not having them installed like Huaweis more recent Smartphone, Amazon's Android devices, Windows new capability for running Android apps as well as privacy friendly Android variants coming without Google Services by design.
The solution for this would be to uses pure Android APIs for the location as detailed e.g. in this blog post: https://fobo66.dev/post/play-services-location-migration/#how-to-request-current-location-with-locationmanager
However given the approaching deadline, I'm not sure if it's reasonable to attempt this now. What do you think?

Originally posted by @violoncelloCH in #373 (review)