v1.18: Fix BankForks::new_rw_arc memory leak (backport of #1893)

[mergify]

Problem

BankForks::new_rw_arc leaks memory because BankForks holds an Arc to a Bank and the Bank holds an Arc to BankForks through the Bank::transaction_processor: TransactionBatchProcessor<BankForks>, TransactionProcessor<FG: ForkGraph>::program_cache: Arc<RwLock<ProgramCache<FG>>>, ProgramCache<FG: ForkGraph>::fork_graph: Option<Arc<RwLock<FG>>> reference cycle.

Summary of Changes

Changed the fork_graph field to pub fork_graph: Option<Weak<RwLock<FG>>> to break the reference cycle. The test_bank_forks_new_rw_arc_memory_leak fails before the bug fix because of leaked threads from thread pools inside AccountsDb.

This bug has been introduced in solana-labs#33776. This bug affects also v1.18 and v1.17.

---

This is an automatic backport of pull request #1893 done by Mergify.

[mergify]

Cherry-pick of d441c0f has failed:

On branch mergify/bp/v1.18/pr-1893
Your branch is up to date with 'origin/v1.18'.

You are currently cherry-picking commit d441c0f577.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   bench-tps/src/bench.rs
	modified:   core/src/banking_stage.rs
	modified:   core/src/banking_stage/decision_maker.rs
	modified:   core/src/banking_stage/read_write_account_set.rs
	modified:   core/src/banking_stage/unprocessed_transaction_storage.rs
	modified:   poh/src/poh_service.rs
	modified:   rpc/src/transaction_status_service.rs
	modified:   runtime/src/bank_client.rs
	modified:   runtime/tests/stake.rs
	modified:   stake-accounts/src/stake_accounts.rs

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   core/benches/banking_stage.rs
	both modified:   core/benches/consumer.rs
	both modified:   core/src/banking_stage/consume_worker.rs
	both modified:   core/src/banking_stage/consumer.rs
	deleted by us:   core/tests/unified_scheduler.rs
	both modified:   ledger/benches/blockstore_processor.rs
	both modified:   ledger/src/blockstore_processor.rs
	both modified:   program-runtime/src/loaded_programs.rs
	both modified:   programs/sbf/tests/programs.rs
	both modified:   runtime/src/bank.rs
	both modified:   runtime/src/bank/tests.rs
	both modified:   runtime/src/bank_forks.rs
	deleted by us:   svm/src/transaction_processor.rs
	deleted by us:   svm/tests/conformance.rs
	deleted by us:   svm/tests/integration_test.rs
	both modified:   unified-scheduler-pool/src/lib.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[pgarg66]

@andreisilviudragnea the cherry-pick to the v1.18 branch has merge conflicts. Would you like to triage it?
Backport to v2.0 was clean. If that's sufficient for your needs, we can abandon this PR.

[andreisilviudragnea]

@pgarg66 I will try to triage it over the weekend.

[t-nelson]

this is not a backport candidate to any branch

[pgarg66]

Closing this PR, as backports to v1.18 is limited to critical fixes.