fix(view): make removeMount locking cleanup exception-safe

[joshtrichards]

• Resolves: #

Summary

Continuing my efforts to eliminate more "lock acquired, then an exception bypasses cleanup" pattern from another spot in the code base.

Make removeMount() release its lock on every exit.

This protects against exceptions from the umount hook, changeLock(), IMovableMount::removeMount(), or post_umount hook.

Also preserves non-cleanup exceptions and passes them on.

Why

removeMount() / movable-mount cleanup is not exception-safe:

• removeMount() acquires a shared mount-point lock, emits an umount hook, promotes the lock to exclusive, calls removeMount(), downgrades, emits the post-hook, then unlocks.
• If a hook, changeLock(), or the mount’s removeMount() implementation throws, neither the downgrade nor unlock is guaranteed. A try/finally should protect that sequence.

TODO

• ...

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