Post conflict resolution for self-hosted sites

[pantstamp]

This PR contains the modifications needed for the new post conflict handling for the self-hosted sites that use XML-RPC calls. We are adding the if_not_modified_since parameter to the wp.edit call so we can get the 409 error code when there is a more recent revision of the post that we try to update.

Specs pcdRpT-5ID-p2#comment-9638.

WP Companion PR: wordpress-mobile/WordPress-Android#20651

To Test:

• Check out trunk branch of the Jetpack and WordPress app. Replace FluxC hash with the one produced by this PR and build.

Test Post version forced write on top of web (existing logic)

• Login with a self-hosted site that has posts. You can create a new self-hosted site using this tool.
• Navigate to Me > Debug Settings
• Disable the sync_publishing flag and restart the app
• Navigate to back to My Site > Post
• Tap the publish tab and then tap a post to open the edit view
• PAUSE - GO TO YOUR LAPTOP
• Open a browser and navigate to the same WordPress site
• Open the same post and make an edit (remember what you changed)
• Tap the "update" button to save it and back out of the editor
• GO BACK TO YOUR DEVICE
• Make a change to the post you have in the edit view
• Tap "Update" to save the post to the server
• ✅ Verify the post did update (snackbar)
• GO BACK TO THE LAPTOP
• Tap view on the same post you just edited via the app
• ✅ Verify the changes you made on the device have overwritten the changes you made on your laptop
• Repeat this test for Jetpack and Wordpress

Test Post version did not write on top of web (new logic)

• Navigate to Me > Debug Settings
• Enabled the sync_publishing flag and restart the app
• Navigate to back to My Site > Post
• Tap the publish tab and then tap a post to open the edit view
• PAUSE - GO TO YOUR LAPTOP
• Open a browser and navigate to the same WordPress site
• Open the same post and make an edit (remember what you changed)
• Tap the "update" button to save it and back out of the editor
• GO BACK TO YOUR DEVICE
• Make a change to the post you have in the edit view
• Tap "Update" to save the post to the server
• ✅ Verify the post did not update and the post list shows "Version Conflict" within the post row
• GO BACK TO THE LAPTOP
• Tap view on the same post you just edited via the app
• ✅ Verify the changes you made on the device did not overwrite the changes you made on your laptop
• Repeat this test for Jetpack and Wordpress

Test Conflict Resolution dialog is shown

• Continue from the last step of test "Post version did not write on top of web (new logic)"
• On the post list, tap on the post that shows "Version Conflict"
• ✅ Verify the conflict resolution overlay is shown
• Tap local version
• ✅ Verify the local version has been applied
• Repeat the scenario in test "Post version did not write on top of web (new logic)" to get into a Version Conflict again. Then repeat this test and tap web version in the conflict resolution dialog.

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Regression Notes

1. Potential unintended areas of impact
   The post is not updated properly

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)
   Relied upon existing automated post tests

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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.

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Testing Checklist (strike-out the not-applying and unnecessary ones): No UI components were changed with this PR

• WordPress.com sites and self-hosted Jetpack sites.

[zwarm]

@pantstamp - Works like a charm.
I left one minor suggestion. It's entirely up to you to decide to implement. 👍