[Quest API] Add apis to end shared tasks (#2521)

This required some minor shared task refactoring

- Shared task expiration handling was moved to world. Previously this
  was handled by zone and had clients self remove when a shared task
  expired. This resulted in wrong messages when a task ended.

- FailTask is now implemented for shared tasks which previously only
  made the client quit the shared task. It now fails the task for all
  members by ending the shared task.

The `Client::EndSharedTask` api will end the client's current shared
task (removing all members). This is similiar to the `FailTask` api
except it doesn't require a `task_id` and the red task fail banner is
optional (live doesn't use it for shared tasks).

The global `end_dz_task` api was added for when a client context isn't
available. This will end a shared task if the current zone is a dynamic
zone for a shared task mission. Currently only shared tasks use dynamic
zones but this api can be expanded if support is added for tasks/quests.

The global `get_dz_task_id` was added to conveniently get the task id
for the current dynamic zone if it's used for a mission. Note this is
a database hit since that information is not available at zone level.

zone/questmgr.cpp

@@ -2480,6 +2480,24 @@ std::string QuestManager::gettaskname(uint32 task_id) {
 	return std::string();
 }
 
+int QuestManager::GetCurrentDzTaskID() {
+	QuestManagerCurrentQuestVars();
+
+	if (RuleB(TaskSystem, EnableTaskSystem) && zone && task_manager) {
+		return task_manager->GetCurrentDzTaskID();
+	}
+
+	return 0;
+}
+
+void QuestManager::EndCurrentDzTask(bool send_fail) {
+	QuestManagerCurrentQuestVars();
+
+	if (RuleB(TaskSystem, EnableTaskSystem) && zone && task_manager) {
+		task_manager->EndCurrentDzTask(send_fail);
+	}
+}
+
 void QuestManager::clearspawntimers() {
 	if (!zone) {
         return;