Prevent leaving unreferenced slabs in storage while updating dictionary with enum key (port internal fix)

[fxamacker]

A bugfix is available to resolve cadence-internal issue:

• Jan 17 issue: cadence-internal issue 187
• July 29 bugfix: cadence-internal PR 242

Please review and consider merging to:

• [ ] Cadence v0.42 mainnet
• [ ] Cadence v1.0 testnet

The bugfix PR (as of July 29, 2024) is about:

• +10 lines for the fix (all in one spot)
• +390 lines for tests and comments

The fix avoids the drawbacks I described for two alternative approaches considered.

Caveats

The condition to trigger the bugfix code can be narrow (original PR) to reduce risk of introducing bugs.

However, as Supun mentioned in PR review feedback, a wider condition (updated PR) can help avoid having to update the condition later if new (relevant) types are added after Cadence 1.0 is deployed.

Both approaches are reasonable and require testing before deployment.

[fxamacker]

@SupunS Many thanks for review, feedback, and approving https://github.com/dapperlabs/cadence-internal/pull/242 earlier this week! :pray:

@turbolent Good to have you back! PTAL at PR https://github.com/dapperlabs/cadence-internal/pull/242 :pray: (when you have time).

[fxamacker]

Closed by #3602.