Refactor request handling

[zachallaun]

The goal of this PR is to make request handling on the server simpler and easier to understand.

The commits are mostly atomic, so reviewing commit-by-commit may be best. Notes on some of the changes:

• Delete Server.Provider.Env, which for a long time has been a struct containing only :project, and instead pass projects directly to handlers. This removes a level of indirection and gets rid of any confusion between it and Ast.Env.
• Delete Server.Provider.Queue.Supervisor in favor of starting a Task.Supervisor explicitly and moving the couple helper functions directly into the module in which they're used.
• Stop converting request IDs to strings. According to the LSP spec, request IDs can be string | integer, but from everything I found, implementations should not consider 1 == "1". If there's a reason we need to do this conversion (e.g. to handle a badly-behaving client), we can add it back in, but it seemed like an unnecessary complication.
• Replace Server.Provider.Queue with Server.TaskQueue, which just operates on IDs and MFAs. This means TaskQueue doesn't have to know or care about handlers. The server now finds the handler for the request before calling TaskQueue.add/2, instead of the queue having to do it. This also means that adding to the queue always succeeds.

[Moosieus]

Tests look good + working for me locally. This is definitely a good stride towards ease-of-contribution.

[scottming]

Delete Server.Provider.Env, which for a long time has been a struct containing only :project, and instead pass projects directly to handlers. This removes a level of indirection and gets rid of any confusion between it and Ast.Env

It is worth noting that we used client_name in the rename PR. So, will we also need to add a client_name field to the Project struct after this pr merged?

[zachallaun]

@scottming What if we remove Server.Provider.Env but, instead of passing project to handlers, we just pass the whole %Server.Configuration{}?

The :client_name comes from the Server.Configuration struct, as does :project. It seems to me that Server.Provider.Env is just a subset, but I don't think we need to hide the configuration struct from modules in the server app.

[zachallaun]

@scottming @Moosieus @scohen I think this should be ready to go. Addressed PR feedback and, based on Scott's comment, updated the first commit to pass %Server.Configuration{} instead of the %Project{} struct to request handlers. This way, Scott can base his rename PR off of this, using the :client_name in the config, and we can still remove an unneeded struct (the %Provider.Env{}).