Synced heap.c/h structure and names with pokeheartgold and pokeplatinum

[AsparagusEduardo]

I previously forgot to make a PR to sync heap functions for pokediamond. This PR accounts for it, while also syncing the contents of the heap.c/heap.h files themselves:

• Renamed instances of heapId to heapID.
• Changed functions:

  pokeplatinum                       | PR                          | pokeheartgold
                                     |                             |
  Heap_InitSystem                    | Heap_InitSystem             | InitHeapSystem
  Heap_Create                        | Heap_Create                 | CreateHeap
  Heap_CreateAtEnd                   | Heap_CreateAtEnd            | CreateHeapAtEnd
  Heap_Destroy                       | Heap_Destroy                | DestroyHeap
  Heap_AllocFromHeap                 | Heap_Alloc                  | AllocFromHeap
  Heap_AllocFromHeapAtEnd            | Heap_AllocAtEnd             | AllocFromHeapAtEnd
  Heap_FndGetTotalFreeSizeForExpHeap | HeapExp_FndGetTotalFreeSize | GF_ExpHeap_FndGetTotalFreeSize
  Heap_FndInitAllocatorForExpHeap    | HeapExp_FndInitAllocator    | GF_ExpHeap_FndInitAllocator
  Heap_ReallocFromHeap               | Heap_Realloc                | ReallocFromHeap
  Heap_FreeToHeap                    | Heap_Free                   | FreeToHeap         
  Heap_FreeToHeapExplicit            | Heap_FreeExplicit           | FreeToHeapExplicit 
  

Matching PRs:

• pokeheartgold:
  • Sync Heap functions with pokeplatinum pokeheartgold#384
  • Fully sync Heap functions with pokeplatinum pokeheartgold#392
  • Synced heap.c/h structure with pokeplatinum and pokediamond pokeheartgold#429
• pokeplatinum:
  • Sync Heap functions with pokeheartgold pokeplatinum#584
  • Fully sync Heap functions with pokeheartgold pokeplatinum#621
  • Synced heap.c/h structure with pokeheartgold and pokediamond pokeplatinum#865