test(files_sharing): cover sharing through multiple mounts

[joshtrichards]

• Resolves comment: [stable34] fix: Creating shares with multiple mount permissions #63372 (review)

Summary

Strengthen coverage for sharing a node reachable through multiple mounts with different permissions.

The previous test did not create multiple accessible paths to the same node and injected PERMISSION_ALL into NodeResource, so it did not exercise permission merging. This version creates and accepts:

• a full-permission parent-folder share
• a read-only direct share of the child

It then verifies that NodeResource::getNodePermissions() merges permissions across both paths and allows the share interaction.

Follow-up to recently merged PR #63299 to improve regression coverage.

TODO

• Backport to same branches as fix: Creating shares with multiple mount permissions #63299 was

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)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[joshtrichards]

/backport to stable34