[CHERRY-PICK] MdeModulePkg: Improved error handling in RuntimeDxe Variable drivers [Rebase & FF]

[PaddyDeng-v]

Description

Cherry-pick of tianocore/edk2 PR #12670 (commit 8bf75267f9311a8a66a3864ee71426c70bb288bb).

This PR improves error handling in the Variable SMM/DXE RuntimeDxe drivers by replacing
ASSERT_EFI_ERROR calls with proper error-returning handling. This ensures platforms with
ASSERT_DEADLOOP_ENABLED disabled handle initialization errors gracefully instead of
silently continuing.

Changes

• Replace ASSERT_EFI_ERROR with if (EFI_ERROR(...)) + DEBUG + goto ErrorExit pattern
• Add comprehensive ErrorExit cleanup paths in VariableServiceInitialize() and MmVariableServiceInitialize()
• Remove inline cleanup from VariableCommonInitialize() error paths (callers handle cleanup)
• Move gEfiVariableArchProtocolGuid installation to end of VariableServiceInitialize()
• Add VariableClearNotifySmmReady() function for SMM notification cleanup

Conflict Resolution

• VariableDxe.c: Preserved mu_basecore's InitializeVariablePolicyLocking call (MU_CHANGE)
  while wrapping it with proper error handling instead of ASSERT_EFI_ERROR.

How This Was Tested

Cherry-picked and conflict-resolved from upstream edk2 where it passed CI.

Integration Checklist

• Impacts functionality?
• Impacts security? (improved error handling)
• Breaking change?
• Includes tests?
• Includes documentation?

[Aaron (apop5)]

PaddyDeng-v

Please amend the commit to contain [Cherry-Pick] in the commit message title.

[Michael Kubacki (makubacki)]

PaddyDeng-v

Please amend the commit to contain [Cherry-Pick] in the commit message title.

Also, same additional request mentioned in #1899 (review).

[PaddyDeng-v]

Hi Michael Kubacki (@makubacki) and Aaron (@apop5) ,

Thanks for reviewing this draft. I created this first because the original edk2 PR was merged after stable tag 202608. But it seems MU_BASECORE's 202608 branch is not ready for PR.
Should I keep this draft and wait for 202608 is ready, or drop this one and we will include it from 202511?

[Michael Kubacki (makubacki)]

Hi Michael Kubacki (Michael Kubacki (@makubacki)) and Aaron (Aaron (@apop5)) ,

Thanks for reviewing this draft. I created this first because the original edk2 PR was merged after stable tag 202608. But it seems MU_BASECORE's 202608 branch is not ready for PR. Should I keep this draft and wait for 202608 is ready, or drop this one and we will include it from 202511?

PaddyDeng-v, this would naturally be cherry-picked onto the 202608 branch for the reason you mentioned. Unless there is a strong reason it's needed in 2511, I suggest sticking to that.

[PaddyDeng-v]

Closing this PR since the change will cherry picked as part of 202611

[Michael Kubacki (makubacki)]

PaddyDeng-v, sorry if there was a misunderstanding, but I believe you should leave this PR open because you want the change in 202608, right? What I meant in "naturally be cherry-picked onto the 202608 branch" in my previous message is that it would be cherry-picked into 2608 (as you've done here) and not 2511 (as you did in the other PR) since 2608 is the upcoming release branch.