MdeModulePkg/Variable/RuntimeDxe: Restore Variable Lock Protocol behavior

MdeModulePkg/Variable/RuntimeDxe: Restore Variable Lock Protocol behavior

https://bugzilla.tianocore.org/show_bug.cgi?id=3111

The VariableLock shim currently fails if called twice because the
underlying Variable Policy engine returns an error if a policy is set
on an existing variable.

This breaks existing code which expect it to silently pass if a variable
is locked multiple times (because it should "be locked").

Refactor the shim to confirm that the variable is indeed locked and then
change the error to EFI_SUCCESS and generate a DEBUG_ERROR message so
the duplicate lock can be reported in a debug log and removed.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Bret Barkelew <Bret.Barkelew@microsoft.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>