Improved file provider switch user experience

[i2h3]

The user experience has not been great since the merge of the classic folder sync and file provider builds. Due to the technical limitations imposed by macOS, both modes cannot operate simultaneously on app level. To communicate this more clearly, this has been reworked.

Checklist

• Sign-off message is added to all commits.
• The commit history is clean with no merge commits.
  • How to rebase your commits
  • How to squash commits with rebase
• Uploaded screenshots from before and after for UI changes.
• Documentation has been updated or is not required.
• Backports requested where applicable (critical bugfixes).
• Labels added where applicable (bug/enhancement).
• Milestone added for target version.

AI (if applicable)

• The content of this PR was partly or fully generated using AI
  • I have read the guidelines for AI-assisted contributions.
  • I have read Nextcloud's AI Contribution Policy.

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-10354.zip

Digest: sha256:4c3e68ec3a532e614907325b5fe4d350d2f53c2a3a213f1b1622a8e16bdfc402

To test this change/fix you can download the above artifact file, unzip it, and run it.

Please make sure to quit your existing Nextcloud app and backup your data.

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot
75.9% Coverage on New Code (required ≥ 80%)
C Reliability Rating on New Code (required ≥ A)
D Security Rating on New Code (required ≥ A)
300 New Code Smells (required ≤ 0)
1 New Bugs (required ≤ 0)
D Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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