Doc editor: Clear selection on defocus (fixes #13538).

[kazcw]

Doc editor: Clear selection on defocus (fixes #13538).

Also: Fix editor defocusing when using its scrollbar.

Pull Request Description

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Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
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• Unit tests have been written where possible.
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  or the Snowflake database integration, a run of the Extra Tests has been scheduled.
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