Support matching bitstrings that are in fact binaries (size divisible by 8)

[mat-hek]

In some cases, there's generic code that uses the bitstring modifier because it needs to work for both bitstrings and binaries, for example in erl_eval. Currently such code doesn't work even if no actual bitstrings are involved, and this PR attempts to fix it. In other words, this now works:

defmodule Foo do
  def pattern_match(x, s) do
    case x do
      <<a::bitstring-size(s), b::bitstring>> ->
        {a, b}

      _ ->
        :no_match
    end
  end
end

Foo.pattern_match(<<234, 123, 2>>, 16)
# => {<<234, 123>>, <<2>>}

TODO:

• [x] add tests
• [x] adjust jit.erl