feat(Core/Unit): New helper IsClass and script hook OnPlayerIsClass (#18243)

* Class Comparison Logic Encapsulation - Parity

* Add Context to IsClass

* Add Unit IsClass script hook

* Replace additional getClass with IsClass

* Update CanUseItem to replace getClass with IsClass

* Add separate context for pet vs ability

* Change Create to Init since not all referenced contexts are creation

* Align spacing in ClassContext

* Drop context on LFGManager max power

* Update IsClass context that wraps around Missle Barrage

* Rename context for swapping weapons

* Be more specific than CLASS_CONTEXT_TALENT

* Remove duplicate context

* Moved IsClass Hook to Player

* Removed unused parameter in virtual base function

* Added maybe_unused to IsClass virtual in order to compile

To match the override signature, the virtual base needs to include the parameter in question, so using [maybe_unused] to signal to the compiler to allow it

* Remove extra blank line

* Add ABILITY_REACTIVE context

* Add context for PET_CHARM

* Remove explicit nullopt check per review

* Code Readability - Change if to if else in pet

Due to the return pattern, this doesn't change functionality in any way

* Add OnPlayer to disambiguate

---------

Co-authored-by: NathanHandley <nathanhandley@protonmail.com>

src/server/scripts/Commands/cs_reset.cpp

@@ -140,7 +140,7 @@ public:
         uint8 oldLevel = playerTarget->GetLevel();
 
         // set starting level
-        uint32 startLevel = playerTarget->getClass() != CLASS_DEATH_KNIGHT
+        uint32 startLevel = !playerTarget->IsClass(CLASS_DEATH_KNIGHT, CLASS_CONTEXT_INIT)
                             ? sWorld->getIntConfig(CONFIG_START_PLAYER_LEVEL)
                             : sWorld->getIntConfig(CONFIG_START_HEROIC_PLAYER_LEVEL);