PSMDB-2023 Abandon snapshot after catalog reopen in FCBIS storage switch

[igorsol]

SERVER-108364 added allowOneUntimestampedWrite() to _updateMinValidDocument which invariants if recovery unit is active.
openCatalogAfterStorageChange() can leave the RU active, so callers that subsequently invoke setMinValid() hit the invariant. Abandon the snapshot before returning from _switchStorageLocation to ensure the RU is inactive.

[github-actions]

Backport Policy Overview

@igorsol, This branch (v8.0) is a production release branch and does not accept direct PRs.
All changes must flow through the corresponding staging branch (v8.0-staging), where they are tested and validated before being promoted into v8.0 by the Server Release team.

Next step: Please re-open this PR against v8.0-staging.

Please reach out in #server-release if you have any questions.

[Copilot]

Pull request overview

This PR prevents setMinValid() callers from hitting an invariant after an FCBIS storage location switch by ensuring the OperationContext’s RecoveryUnit is no longer in an active snapshot/WT transaction state after openCatalogAfterStorageChange().

Changes:

• Abandon the current recovery unit snapshot after catalog::openCatalogAfterStorageChange(opCtx) in _switchStorageLocation().
• Add an explanatory comment describing why the snapshot must be abandoned before subsequent setMinValid() calls.

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