Set Parent from Pages screen also publishes all Local Changes

[thomashorta]

This possible issue / improvement opportunity was found while I was implementing PR #17329, and was mentioned briefly on that PR description and comments.

Basically: when the parent of a page with local changes (in content for example) is changed using the "Set Parent" option from the Pages screen, then the local changes are also published, and not just the parent page setting.

Expected behavior

I am not 100% sure of what I would expect in this scenario, but I have a few ideas:

1. Update ONLY the parent page setting. (which looks a bit more challenging to implement)
2. Show a confirmation dialog to the user saying all pending local changes will also be saved and updated.
3. Disable / remove that "Set Parent" option from that page item overflow menu when there are local changes to it.

Actual behavior

No information is shown about updating all local changes, and it just updates everything that changed + the parent page, so when I go to the actual published page, I notice the local changes I made to other settings / content were also updated.

Video with the steps and current behavior

bug_set_parent_push_changes_small.mp4

Steps to reproduce the behavior

0. Open the WordPress Android app and log into an account that has at least 2 top-level pages
1. In the Home screen, make sure you are on the My Site > Menu page
2. Tap on the "Pages" option
3. In the Pages screen, tap on any page to go to the editor
4. In the Editor, make any changes
5. Hit back to save the changes locally
6. Check that the page, in the Pages screen, shows a label saying there are "Local Changes"
7. Hit back one more time to go to the home screen
8. Tap your site URL to see it's current "published" version
9. Go to the page where you made the changes
10. Verify that the changes ARE NOT there (since they are only local)
11. Hit back again to go to the home screen
12. Make sure you are on the My Site > Menu page
13. Tap on the "Pages" option
14. In the Pages screen, tap on overflow menu ("⋮", three vertical dots) for the page that has local changes
15. Tap on the "Set parent" option
16. Select a new parent page
17. Tap on Save, on the top bar
18. Check that the page was saved and "Local Changes" label is not there anymore
19. Check that a snackbar saying "Page updated" is shown
20. Repeat steps 7-9
21. Verify that the previous local changes ARE there now

Tested on Samsung S21+, Android 12, WPAndroid 21.0-rc01

Also tested on the Android emulator, Android 12, during development of #17329, not sure what WPAndroid version but < 21