[BATTC] Signal the wait battery tag event when notifying Battery Class

BatteryClassStatusNotify is used by battery miniport drivers to notify the Battery Class of a status change. This can either be a battery status change or battery tag assignation, depending on what the device extension (namely the composite battery) waits for.

We do have implementation for EVENT_BATTERY_STATUS but not for EVENT_BATTERY_TAG. What happens is when BatteryClassIoctl fails to query the battery tag because it has not yet been assigned, the thread is stuck on waiting for the event object to be signaled, forever.
This tipically happens when a timeout of -1 (meaning the calling thread must wait indefinitely) is supplied. The composite battery driver (COMPBATT) is responsible to signal the Battery Class when a CM (Control Method) ACPI battery receives a tag, which then this function will signal the event.

CORE-18969
CORE-19452

drivers/battery/battc/battc.c

@@ -76,11 +76,13 @@ BatteryClassQueryWmiDataBlock(PVOID ClassData,
 BCLASSAPI
 NTSTATUS
 NTAPI
-BatteryClassStatusNotify(PVOID ClassData)
+BatteryClassStatusNotify(
+    _In_ PVOID ClassData)
 {
     PBATTERY_CLASS_DATA BattClass;
     PBATTERY_WAIT_STATUS BattWait;
     BATTERY_STATUS BattStatus;
+    ULONG Tag;
     NTSTATUS Status;
 
     DPRINT("Received battery status notification from %p\n", ClassData);
@@ -99,7 +101,14 @@ BatteryClassStatusNotify(PVOID ClassData)
     {
         case EVENT_BATTERY_TAG:
             ExReleaseFastMutex(&BattClass->Mutex);
-            DPRINT1("Waiting for battery is UNIMPLEMENTED!\n");
+            Status = BattClass->MiniportInfo.QueryTag(BattClass->MiniportInfo.Context,
+                                                      &Tag);
+            if (!NT_SUCCESS(Status))
+                return Status;
+
+            ExAcquireFastMutex(&BattClass->Mutex);
+            KeSetEvent(&BattClass->WaitEvent, IO_NO_INCREMENT, FALSE);
+            ExReleaseFastMutex(&BattClass->Mutex);
             break;
 
         case EVENT_BATTERY_STATUS: