References provider fails to find function arguments

[lukaszsamson]

The following test fails

test "find references of variables in arguments" do
    buffer = """
    defmodule MyModule do
      def call(conn) do
        if true do
          conn
        end
      end
    end
    """

    references = ElixirSense.references(buffer, 2, 13)

    assert references == [
      %{range: %{end: %{column: 16, line: 2}, start: %{column: 12, line: 2}}, uri: nil},
      %{range: %{end: %{column: 11, line: 4}, start: %{column: 7, line: 4}}, uri: nil},
    ]
    # returns []
  end

The reason is broken variable tracking in MetadataBuilder.State. new_func_vars_scope works differently from new_vars_scope - it does not increment the scope_id counter and thanks to that conn variable is not in the function scope. The second problem is subscope handling. When leaving a subscope in remove_vars_scope all subscope variable positions are lost.