Fix extracted line numbers

[FedorSherbakov]

A couple of fixes:

embeddedJS

Change way of extracting embedded JS to look for "#text" nodes, as serializer drops original line breaks and results with wrong line numbers

Such example was giving wrong line numbers:

<div>
  <button
    class="something"
    type="button"
  >
    {{ $gettext('Hello there!') }}
  </button>
</div>

attributeEmbeddedJS

Prevent scope leak for lineNumberStart variable, so result is correct for all attributes in tag, not only the first one

Such example was giving wrong line numbers:

<button
  class="something"
  v-text="$gettext('Hello there!')"
/>

[FedorSherbakov]

Hi @lzurbriggen!

Could you take a look please? This one pretty much reduces noise in po files 🙂

[jeremyzahner]

@lzurbriggen LGTM.