Should allow user to undo changes made to a rule even after switching to another rule in rule list UI.

[RaymondLim]

1. Open an inline editor that has at least two css rules.
2. Make some changes to the currently selected rule.
3. Select another rule from rule list UI just like a real user is locating the right css rule.
4. Pretend that changes have made to the wrong rule, so select the rule that has some changes in step 2.
5. Press Ctrl+Z to undo.

Result: you can't. You can only undo in the css file if you have that file open. Otherwise, you have to manually revert your changes if you still remember those changes.

[peterflynn]

Adding to 'to user story' tag. The Undo story for Editor-Document syncing hasn't happened yet, so this is technically out of scope from sprint 6. However, IIRC the original assumption in sprint 6 was that inline Editors would be 'cached' in the inline widget after being created, instead of being disposed as soon as the user switches to a different rule (similar to how full-size Editors for working set entries are kept around). If it was implemented that way, this particular Undo bug would go away.

Does QRB maybe want to make a call on this one?

[njx]

QRB reviewed

[pthiess]

Added to BS --> #299178