suggestion: Omit behaviour `impl` declarations from document symbols

[leonqadirie]

The current implementation of document symbols (subjectively) feels cluttered if a module contains many impl declarations.

So given this snippet:

  use GenServer

  @impl GenServer
  def init(arg) do
    {
      :ok,
      arg,
      {:continue, :noop}
    }
  end

  @impl GenServer
  def handle_continue(
        :noop,
        arg
      ) do
    :ok
  end

I suggest to only provide the document symbols

def init(arg)
def handle_continue(:noop, arg)

instead of

@impl GenServer
def init(arg)
@impl GenServer
def handle_continue(:noop, arg)