Add Array.ID() and OrderedMap.ID()

[fxamacker]

Issue To Be Solved

Currently Array.StorageID() and OrderedMap.StorageID() are used as identifier in client because storage IDs are guaranteed to unique. However, storage ID should be only used to retrieve slabs (registers) from storage.

Also, when Atree register inlining is implemented in the future, some resources may not be stored in separate slabs, so they will not have storage IDs anymore.

Suggested Solution

Add ID() to uniquly identify Array and OrderedMap. For now, implement ID to be identical to StorageID in raw bytes ([16]bytes). In the future, this can be changed to be decoupled from storage ID completely.

Once ID() is available, clients should use it instead of StorageID() to identify Atree composite values.