init: rename 'Trigger' to 'Event' and convert to std::variant

The term 'trigger' should be used in 'Action' to indicate what causes
the 'Action' to be executed.

The term 'event' should be used in ActionManager's queue to indicate
a state change that is checked against the 'triggers' of an 'Action' to
see if it should execute.

Convert the previous Trigger class to std::variant, as the latter is
better suited for this use.

Change-Id: I2558367c8318b536aa69fcec93793f1c12857ef5
diff --git a/init/init.cpp b/init/init.cpp
index e91faea..99ce5e6 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -164,8 +164,8 @@
     // waiting on a property.
     if (name == "sys.powerctl") HandlePowerctlMessage(value);
 
-    if (property_triggers_enabled)
-        ActionManager::GetInstance().QueuePropertyTrigger(name, value);
+    if (property_triggers_enabled) ActionManager::GetInstance().QueuePropertyChange(name, value);
+
     if (waiting_for_prop) {
         if (wait_prop_name == name && wait_prop_value == value) {
             wait_prop_name.clear();
@@ -535,7 +535,7 @@
 static int queue_property_triggers_action(const std::vector<std::string>& args)
 {
     ActionManager::GetInstance().QueueBuiltinAction(property_enable_triggers_action, "enable_property_trigger");
-    ActionManager::GetInstance().QueueAllPropertyTriggers();
+    ActionManager::GetInstance().QueueAllPropertyActions();
     return 0;
 }