Don't hide inline assist when editor loses focus (#12990)

Release Notes:

- Now when an editor loses focus (e.g. from switching tabs) and then
gains focus again, it doesn't close the inline assist. Instead, it only
closes when you move the cursor outside of it, e.g. by clicking
somewhere else in its parent editor.

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Co-authored-by: Antonio Scandurra <me@as-cii.com>