Update the Web A11Y DOM without rebuilding unchanged nodes (#3349)

This PR is a pre-requisite for fixing scroll -
https://youtrack.jetbrains.com/issue/CMP-8627/Web-A11y.-Voice-over.-Scroll-doesnt-work

Previously we had this on every sync:

```
// To ensure the correct order of nested nodes, we remove all of them.
// I assume it's more efficient to remove and re-add them than to insert the nodes at specific positions.
// Also, the code is more simple with this approach.
// They are added back when they are synced.
removeAllChildrenOf(htmlNode)
```

Now:
By avoiding the unnecessary structural changes in the A11Y tree we
ensure the VO/AT do not loose the focused/active UI element. Otherwise,
on every sync it falls back to activating the nearest "stable" group
element (container) and the AT user has to navigate to the previous
location again.

## Testing
- Added new tests checking the mutations in the A11Y tree

## Release Notes
N/A

Author: eymar