Fix selection shifting when deleting paragraphs on android

[waynetee]

Description

Fixes #4340

This is a second attempt to fix the abovementioned bug, following the unsuccessful attempt in #7122 (apologies for the issues introduced then)

In this PR, selection is only restored during deletion and when several other criteria have been met, this should minimise the chances of any unintended side effects.

Test plan

Before

screen-20250224-160048.mp4

After

screen-20250224-160326.mp4

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[etrepum]

I think the ideal approach here is to come up with a solution that does not depend on setTimeout. This kind of solution causes a lot of trouble down the line with debugging, possibly creating extra history entries, etc. even when it does work.

[waynetee]

@etrepum I agree with you that in a ideal world we would not need to use to use setTimeout. I did spend a significant amount of time investigating this issue and as far as I can tell originates from the browser, making a clean fix difficult.

I see a few ways forward:

1. We merge this PR
2. Rather than using setTimeout in the beforeinput handler, we apply the fix in the selectionchange handler. This is workable, but requires a way to sync it to the deletion event. We would likely end up with a fix not much cleaner than this and might end up having to use setTimeout anyways.
3. We solve the problem in the browser itself, this would be ideal, but it doesn't seem like any progress has been made on the issue since it was filed early last year https://issues.chromium.org/issues/331320419
4. You or someone else volunteers to investigate this issue to try to come up with a better fix. I would be happy to assist in this case.

I personally think this is a significant bug, it would be good if we can resolve it in a timely manner.

[etrepum]

Approach 2 is preferable. I understand that you’ve spent a lot of time investigating, but this type of solution only makes things worse the next time something has to be investigated. Untangling the selection implicit state machine is something on my list but I can’t make any commitments on timing. As you know, this is not simple.

[etrepum]

As far as I can tell with a Google Pixel 5 on Sauce Labs this build still has the bug

[waynetee]

Turns out the fix was skipped over by an earlier optimisation in certain cases. It should be fixed now, and I have tested it on both Pixel and Samsung, and with the SwiftKey keyboard too.

Thanks for helping to test this thoroughly.

[etrepum]

This works with the Pixel and Samsung devices I tried on browser stack with the google, samsung and microsoft keyboards. Does anyone else want to give this a test before merge? /cc @zurfyx @potatowagon