Move some generic test stuff out of the rust-analyzer crate

[Veykril]

Currently regenerating the config, docs and some other stuff require building and running the rust-analyzer crate tests. This is annoying for people contributing fixes just in those places because they'll have to build the entire project and also figure out that they even have to do this in the first place. Additionally, if tidy fails, it will do so after having run all tests on CI which means you are effectively waiting minutes for CI only to realize you forgot a dbg! somewhere later.