リザーブしたシステムメモリの量を返します。
Unity requests the amount of memory that the game will use. GetTotalReservedMemory
is the full amount that Unity currently has. Part of this memory is used by the
game using GetTotalAllocatedMemory, and the remainer is stored and
unused.
See Also: GetTotalAllocatedMemory, GetTotalUnusedReservedMemory.