Server integration tests, support workspace directory

[kubukoz]

Adds a couple basic integration tests by running the language server in a resource directory and having it respond to a couple generic LSP requests.

Also makes the server aware of workspaceDirectories provided in the initialize request (so far using just the first one in the list).

TODO:

• completion provider
• diagnostic provider
• command provider: run command
  • this and the code lens should exercise real HTTP requests to a server also managed by this. Include ember-server and make assertions on the output reported to the client.
  • happy path is enough (when it comes to validating the request), more fine-grained tests can be written as tests for the specific command provider
• custom request (smithyql.runQuery)
• code lens provider
• document symbol provider
• example involving workspace refresh (e.g. adding a new service to the scope and checking that its services can be used without errors)