Add file watcher

When VS Code opens a file, it requests that file be watched, so any changes can be reflected in the editor. Currently, file watching isn't implemented.

Once this is complete, the client will be able to fully support remote filesystem operations.

The file watcher should be able to store watched files, send a command to VS Code when a watched file is modified, and also stop watching files when receiving the stopWatch command.

Here is an example of the command that could be sent to VS Code to notify it of file changes.

---@enum vscode.FileChangeType
local FileChangeType = {
  Changed = 1,
  Created = 2,
  Deleted = 3
}

Connection:send({
  command = "fileChanged",
  payload = {
    type = FileChangeType.Deleted
    path = "example/file.lua"
  }
})