Update support for Tagged PDF

The [explainer for Tagged PDF](https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/PDF/TaggedPDF/explainer.md) only refers to the 16-year-old and outdated PDF 1.7 specification, ISO 32000-1:2008. Edge also needs to support the latest PDF 2.0, ISO 32000-2:2020 (available at no cost from [here](https://pdfa.org/sponsored-standards/).