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Creation of ForEach Blueprint Nodes for TMap and TSet Data Types

Github PR links

• https://github.com/EpicGames/UnrealEngine/pull/10355
• https://github.com/EpicGames/UnrealEngine/pull/11622

TL; DR

1. @MagForceSeven had previously worked on a similar feature for TMap and submitted a PR for it.
2. I felt the need for a Blueprint ForEach node for TSet, so I worked on that separately.
   • During this, I implemented helper functions like GenericSet_Get and GenericSet_LastIndex to allow index-based iteration. This code inspired @MagForceSeven to revise the original TMap implementation based on it.
3. @MagForceSeven later consolidated all of this into a dedicated plugin. Notably, all the Blueprint K2_Node generation work was done solely by him.
   • A logical bug in the previous implementation was also addressed:
   • Bug: Since both TSet and TMap use sparse arrays, adding and removing elements can leave empty slots. To skip over these and access only valid indices, we need to use TScriptContainerIterator, created via FScriptSetHelper.CreateIterator(). The actual physical index can then be retrieved with TScriptContainerIterator.GetInternalIndex().
4. Finally, the whole thing was reviewed and merged into the main branch by Epic Games developer @EpicDaveJones.