Feature request: better navigation of slide mode based on pdfpc metadata

[OrangeX4]

We can implement navigation features like pdfpc in Typst Preview:

• Use up / down keys to navigate through logical slides instead of subslide or animations.
• Use End key to navigate to the end slide.
• Use Shift + M shortcut to navigate to the saved slide.

However, these features require the ability to get the full pdfpc file metadata directly from polylux, rather than the metadata used only by polylux, which requires the additional use of binary polylux2pdfpc.

So I've come up with a script to get the full pdfpc metadata directly in typst, and I'll try to open a PR for polylux.

https://typst.app/project/rzIE9aLpKytQUQNn8SSRrP