Go back to example page with browser Back-button

[emilk]

What

• Closes Web viewer navigation (back-button) #5398

This uses the History API to manipulate the web history.

When leaving the example page, two entries in the history are added:

• ?examples (shows the examples)
• ?url=https://….rrd (the url for the example)

This is then parsed on popstate. We thus support both going forward and back in history.

This is not perfect, but a lot better than before.

Best reviewed commit by commit.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: rerun.io/viewer
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

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