MdeModulePkg/SMM: Support to unregister SMI handler in SMI handlers

This patch fix a use-after-free issue where unregistering an
SMI handler could lead to the deletion of the SMI_HANDLER while it is
still in use by SmiManage(). The fix involves modifying
SmiHandlerUnRegister() to detect whether it is being called from
within the SmiManage() stack. If so, the removal of the SMI_HANDLER
is deferred until SmiManage() has finished executing.
Additionally, due to the possibility of recursive SmiManage() calls,
the unregistration and subsequent removal of the SMI_HANDLER are
ensured to occur only after the outermost SmiManage() invocation has
completed.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>

Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>

MdeModulePkg/Core/PiSmmCore/PiSmmCore.h

@@ -93,6 +93,7 @@ typedef struct {
   SMI_ENTRY                       *SmiEntry;
   VOID                            *Context;    // for profile
   UINTN                           ContextSize; // for profile
+  BOOLEAN                         ToRemove;    // To remove this SMI_HANDLER later
 } SMI_HANDLER;
 
 //