[Site Design Revamp] Fix blank theme preview after orientation change

[mkevins]

Fixes #16672

Description

This PR saves the instance state for the home page picker's view model to the fragment bundle, since that is what the fragment loads from when it restarts.

To test:

Follow the steps on the issue description to try to reproduce: #16672

Expect that the preview is loaded properly after an orientation change event.

Note:

I have not tested whether we can remove this line which writes to the activity bundle. In my testing, this resolved the issue, but if removing that line does not introduce regressions, it may be a minor optimization to consider along with these changes.

Regression Notes

1. Potential unintended areas of impact
   None

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[mkevins]

I've removed the line that writes the theme picker vm to the activity's bundle. Thanks for testing this Antonis!

[antonis]

Great work @mkevins 👍
Thank you for investigating this and coming up with a clear solution. I've tested the fix on a Pixel 5 (Android 12) and it works as expected. The code changes also look consistent too me 🎉

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APKs:

• Jetpack-pr-16700-build-124773.apk

• WordPress-pr-16700-build-124773.apk