Replace ´tempest/core´ with Mapper’s direct dependencies

[steffans]

Description

I noticed tempest/mapper does not use any Tempest\Core* APIs. Its tempest/core requirement only provides access to Container, Discovery, Reflection and Support. Could the tempest/core dependency be removed and the packages required directly instead. This would also be great for the tempest/database package which requires tempest/mapper and therefore would be independent of the tempest/core. It also avoids installing Core's additional dependencies like vlucas/phpdotenv, symfony/cache and filp/woops.

Thanks, for considering. I like the composability of Tempest, so i can choose what packages i really need.

[brendt]

For sure! Feel free to send a PR :)