A Few bugs with Metals integration

I can submit a PR if people agree on what's required. Here are the issues:

1. `ale_linters/scala/metals.vim` tries to use a binary called `metals-vim`, but that's not what the binary is called (anymore at least.) It's just `metals`.
2. The root search code looks for `build.sc`, `build.sbt`, `.bloop`, and `.metals` using `ale#path#ResolveLocalPath`, but it looks like that function is only able to look for files, and `.bloop` and `.metals` are directories, so I think it's just the wrong function. What's the more correct function to use?