message: Allow slide number to be set as bold
  Handle bold from TextBaseProps by setting `b="1"` in the XML. Move up
  align definition before the field as it was no longer working when
  combined with bold.
  Add actual slide number in the XML so that LibreOffice displays the
  slide number too (actually solves
diff: @@ -756,12 +756,13 @@ function slideObjectToXml(slide: PresSlide | SlideLayout): string {
  strSlideXml += '</a:defRPr>'
  }
  strSlideXml += '</a:lvl1pPr></a:lstStyle>'
  - strSlideXml += `<a:p><a:fld id="${SLDNUMFLDID}" type="slidenum"><a:rPr lang="en-US"/>`
  + strSlideXml += '<a:p>'
  if (slide._slideNumberProps.align.startsWith('l')) strSlideXml += '<a:pPr algn="l"/>'
  else if (slide._slideNumberProps.align.startsWith('c')) strSlideXml += '<a:pPr algn="ctr"/>'
  else if (slide._slideNumberProps.align.startsWith('r')) strSlideXml += '<a:pPr algn="r"/>'
  else strSlideXml += `<a:pPr algn="l"/>`
  - strSlideXml += `<a:t></a:t></a:fld><a:endParaRPr lang="en-US"/></a:p>`
  + strSlideXml += `<a:fld id="${SLDNUMFLDID}" type="slidenum"><a:rPr b="${slide._slideNumberProps.bold ? 1 : 0}" lang="en-US"/>`
  + strSlideXml += `<a:t>${slide._slideNum}</a:t></a:fld><a:endParaRPr lang="en-US"/></a:p>`
  strSlideXml += '</p:txBody></p:sp>'
  }
  