Auto merge of #123327 - BoxyUwU:param_env_docs_rewrite, r=compiler-errors

Update `ParamEnv` docs

There is now a wealth of information in the dev guide about `ParamEnv` so we should explicitly link to it from the doc comments. I also added a caution against using `ParamEnv` and removed the comment about it being "suitable for type checking" as you should practically never use `ParamEnv::empty` for type checking

r? `@compiler-errors`

Author: bors