CBL-5077 : Fix close database could hang waiting for active component…

…s to close (#3227)

* Cherry-Pick the fix (7daff8e) from lithum branch.

* When signal the database thread to wake up and check for the close, the close condition needs to be locked first to avoid race condition.

Objective-C/CBLDatabase.mm

@@ -1124,9 +1124,11 @@ - (void) addActiveStoppable: (id<CBLStoppable>)stoppable {
 - (void) removeActiveStoppable: (id<CBLStoppable>)stoppable {
     CBL_LOCK(_mutex) {
         [_activeStoppables removeObject: stoppable];
-
-        if (_activeStoppables.count == 0)
+        if (_activeStoppables.count == 0) {
+            [_closeCondition lock];
             [_closeCondition broadcast];
+            [_closeCondition unlock];
+        }
     }
 }