editor: Fix indention guides and code folding for cloned editors

[rear1019]

Description of Changes

This PR fixes non-working/non-updating indention guides and code folding for cloned editors. A more detailed description/commit message will be added later.

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

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rear1019

[rear1019]

@spyder-devs I forgot about this PR. Are you still interested? If so, I can rebase against current 5.x and provide information about the fix. Please note that this PR is intended for version 5 (milestone is set to version 6). As far as Spyder 6 is concerned, the PR is either obsolete or must be adapted after #21669 is merged.