Prepublishing Nudges : Fixed issue where rotating device would cause new tag to not persist

[jd-alexander]

Fixes #12224

Solution

The EditPostRepository needs to be set beforeisStarted is called because when rotation takes place the ViewModel instance is retained thus it's already started. Nonetheless, the EditPostRepository reference needs to be set to the ViewModel

Testing

1. Open any post for editing.
2. Add some tags.
3. Rotate the device.
4. Observe that previously entered tags remain visible.
5. Add a new tag to the list (after the device was rotated).
6. Tap the left arrow to go back or X to close the tag editor.
7. Observe that all the tags that have been added exist.

Reviewing

Only 1 reviewer is needed but anyone can review.

Submitter Checklist

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.
• I have considered adding accessibility improvements for my changes.
• If it's feasible, I have added unit tests.

[peril-wordpress-mobile]

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

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[malinajirka]

Thanks for the review! Btw it seems the milestone is set to 15.2, but the target branch is 15.1. Should we update the milestone for consistency?