Move ivert logic and trigger logic into Trigger

The base Trigger class is now responsible for inverting the trigger
state and also for signaling trigger activation to the target/indicator.

In addition the following non-function changes also occured:
 - The triggers moved into their own directory
 - The trigger code has been annotated to help lua-language-server
   deduce type information
 - AuraTrigger was moved into its own file

All these changes should make future development of other triggers easier

src/types/unitframe.lua

@@ -19,10 +19,13 @@ local types = omif.GetModule("types")
 local StatusBar = types.StatusBar
 local AuraList = types.AuraList
 local SquareIndicator = types.SquareIndicator
+
+---@class AuraTrigger
 local AuraTrigger = types.AuraTrigger
 
-types.UnitFrame = types.CreateClass("UnitFrame")
-local UnitFrame = types.UnitFrame
+---@class UnitFrame
+local UnitFrame = types.CreateClass("UnitFrame")
+types.UnitFrame = UnitFrame
 
 
 local colors = {
@@ -83,19 +86,20 @@ function UnitFrame:CreateTriggers(triggers)
     for _, trigger in ipairs(triggers) do
         local kind = trigger.kind
         if kind == "AuraTrigger" then
-            self.auras:AddTrigger(
-                AuraTrigger:new(
-                    self:CreateIndicator(trigger.indicator),
+            local indicator = self:CreateIndicator(trigger.indicator)
+            local at = AuraTrigger:new(
                     trigger.spellId,
                     trigger.own,
                     trigger.requiredCount,
                     trigger.invert
-                )
             )
+            at:SetTarget(indicator)
+            self.auras:AddTrigger(at)
         end
     end
 end
 
+
 function UnitFrame:CreateIndicator(indicator)
     local kind = indicator.kind
     if kind == "SquareIndicator" then