Unexport SlabID fields to prevent misuse

[fxamacker]

Updates #296 #292 onflow/flow-go#1744
Updates onflow/cadence#2622 and more context at onflow/cadence#2622 (comment).

Description

Previously SlabID had two exported fields Address and Index. Address field was used in Cadence repo to obtain storage address.

We want clients to obtain storage address by calling Array.Address() or OrderedMap.Address(). This PR unexports Address field to prevent misuse.

---

• Targeted PR against main branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #323 (33b8013) into fxamacker/rename-id-and-related-functions-and-types (adcd6fa) will decrease coverage by 0.10%.
The diff coverage is 80.95%.

@@                                   Coverage Diff                                   @@
##           fxamacker/rename-id-and-related-functions-and-types     #323      +/-   ##
=======================================================================================
- Coverage                                                64.74%   64.64%   -0.10%     
=======================================================================================
  Files                                                       14       14              
  Lines                                                     8046     8050       +4     
=======================================================================================
- Hits                                                      5209     5204       -5     
- Misses                                                    2160     2168       +8     
- Partials                                                   677      678       +1     

Impacted Files	Coverage Δ
array.go	69.92% <71.42%> (ø)
map.go	66.78% <80.00%> (-0.10%)	⬇️
storage.go	74.17% <81.81%> (-0.79%)	⬇️
basicarray.go	49.78% <100.00%> (ø)
storable.go	54.41% <100.00%> (ø)

[turbolent]

👌