Replace HookAddonOrVariable with an EventUtil-based HookAddon

The polling lurker frame is gone. HookAddon gates on
C_AddOns.DoesAddOnExist, waits for PLAYER_LOGIN with
EventUtil.ContinueOnPlayerLogin, then runs on
EventUtil.ContinueOnAddOnLoaded. Addons loaded at startup still hook
only after every pfUI module and skin exists and after the addon's
own VARIABLES_LOADED setup. Load-on-demand addons still hook on their
ADDON_LOADED.

The "or variable" form is gone. Callers that passed a global now pass
the addon that defines it: TheoryCraft, SuperMacro, DPSMate and
Turtle_GroupUI. DPSMate names its windows from its settings, so its
hook now checks for DPSMate_DPSMate itself, as the variable lookup
used to. eqcompare's Guda check uses HookAddon too.

modules/eqcompare.lua

@@ -135,11 +135,9 @@ pfUI:RegisterModule("eqcompare", function ()
   -- spot. Reading the rect inside the Set* call picks the side against the
   -- position the tooltip is about to leave, so place the compare a frame later.
   local deferred
-  if C_AddOns.DoesAddOnExist("Guda") then
-    EventUtil.ContinueOnAddOnLoaded("Guda", function()
-      deferred = true
-    end)
-  end
+  HookAddon("Guda", function()
+    deferred = true
+  end)
 
   local function makeHook(getter)
     return function(tooltip, arg1, arg2, arg3)