fix(files_sharing): Return focus to trigger element on sharing details close

[Pytal]

• For [BITV]: Focus won't return to the details panel after sharing details were closed  #42958

Summary

• Switch v-if to v-show to preserve same instance of return focus element instead of mounting a new element on close
• Return focus to triggering element

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[Pytal]

Tip: Hide whitespace 😉

[Pytal]

/backport 22ab251 to stable28