CWallet::MarkConflicted may acquire the cs_main lock after CWalletDB::LoadWallet acquires the cs_wallet lock during wallet initialization. (CWalletDB::LoadWallet calls ReadKeyValue which calls CWallet::LoadToWallet which calls CWallet::MarkConflicted). This is the opposite order that cs_main and cs_wallet locks are acquired in the rest of the code, and so leads to POTENTIAL DEADLOCK DETECTED errors if bitcoin is built with -DDEBUG_LOCKORDER. This commit changes CWallet::LoadWallet (which calls CWalletDB::LoadWallet) to acquire both locks in the standard order. It also fixes some tests that were acquiring wallet and main locks out of order and failed with the new locking in CWallet::LoadWallet. Error was reported by Luke Dashjr <luke-jr@utopios.org> in https://botbot.me/freenode/bitcoin-core-dev/msg/90244330/
Backport of core PR11126