update documentation for optional references

[dsainati1]

For #1690

Update the documentation on optional references to reflect the changes in #1303.

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• Targeted PR against master 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

[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit 16c5038
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -benchmem -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Results

	old.txt	new.txt
	time/op		delta
CheckContractInterfaceFungibleTokenConformance-2	156µs ± 2%	158µs ± 3%	~	(p=0.445 n=7+6)
ContractInterfaceFungibleToken-2	47.9µs ± 3%	47.8µs ± 3%	~	(p=0.945 n=6+7)
InterpretRecursionFib-2	3.20ms ± 2%	3.20ms ± 3%	~	(p=1.000 n=6+7)
NewInterpreter/new_interpreter-2	1.26µs ± 3%	1.27µs ± 2%	~	(p=0.477 n=7+7)
NewInterpreter/new_sub-interpreter-2	2.65µs ± 1%	2.76µs ± 9%	~	(p=0.101 n=6+7)
ParseArray-2	10.0ms ± 2%	10.1ms ± 2%	~	(p=0.128 n=7+7)
ParseDeploy/byte_array-2	15.5ms ± 4%	15.4ms ± 3%	~	(p=0.710 n=7+7)
ParseDeploy/decode_hex-2	1.32ms ± 3%	1.33ms ± 3%	~	(p=0.535 n=7+7)
ParseFungibleToken/With_memory_metering-2	239µs ± 4%	241µs ± 5%	~	(p=0.456 n=7+7)
ParseFungibleToken/Without_memory_metering-2	185µs ± 5%	184µs ± 3%	~	(p=0.805 n=7+7)
ParseInfix-2	8.68µs ± 2%	8.83µs ± 4%	~	(p=0.165 n=7+7)
QualifiedIdentifierCreation/One_level-2	3.08ns ± 2%	3.07ns ± 2%	~	(p=0.874 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	161ns ± 1%	161ns ± 3%	~	(p=1.000 n=7+7)
RuntimeFungibleTokenTransfer-2	1.24ms ±29%	1.35ms ±20%	~	(p=0.620 n=7+7)
RuntimeResourceDictionaryValues-2	7.36ms ± 1%	7.27ms ± 2%	~	(p=0.234 n=6+7)
Transfer-2	102ns ± 2%	103ns ± 1%	~	(p=0.455 n=7+5)
	alloc/op		delta
CheckContractInterfaceFungibleTokenConformance-2	66.3kB ± 0%	66.3kB ± 0%	~	(p=1.000 n=7+7)
ContractInterfaceFungibleToken-2	26.7kB ± 0%	26.7kB ± 0%	~	(all equal)
InterpretRecursionFib-2	1.25MB ± 0%	1.25MB ± 0%	~	(p=0.727 n=6+6)
NewInterpreter/new_interpreter-2	872B ± 0%	872B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.38kB ± 0%	1.38kB ± 0%	~	(all equal)
ParseArray-2	2.83MB ± 2%	2.81MB ± 2%	~	(p=0.684 n=7+7)
ParseDeploy/byte_array-2	4.46MB ± 3%	4.50MB ± 4%	~	(p=0.383 n=7+7)
ParseDeploy/decode_hex-2	214kB ± 0%	214kB ± 0%	~	(p=0.343 n=7+7)
ParseFungibleToken/With_memory_metering-2	36.3kB ± 0%	36.3kB ± 0%	~	(p=1.000 n=7+7)
ParseFungibleToken/Without_memory_metering-2	36.3kB ± 0%	36.3kB ± 0%	~	(p=0.070 n=7+7)
ParseInfix-2	2.17kB ± 0%	2.17kB ± 0%	~	(p=0.179 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
RuntimeFungibleTokenTransfer-2	236kB ± 0%	237kB ± 0%	~	(p=0.073 n=6+7)
RuntimeResourceDictionaryValues-2	2.25MB ± 0%	2.25MB ± 0%	~	(p=0.805 n=7+7)
Transfer-2	48.0B ± 0%	48.0B ± 0%	~	(all equal)
	allocs/op		delta
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	460 ± 0%	460 ± 0%	~	(all equal)
InterpretRecursionFib-2	23.8k ± 0%	23.8k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	12.0 ± 0%	12.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	40.0 ± 0%	40.0 ± 0%	~	(all equal)
ParseArray-2	70.0k ± 0%	70.0k ± 0%	~	(all equal)
ParseDeploy/byte_array-2	105k ± 0%	105k ± 0%	~	(p=0.538 n=6+7)
ParseDeploy/decode_hex-2	78.0 ± 0%	78.0 ± 0%	~	(all equal)
ParseFungibleToken/With_memory_metering-2	1.06k ± 0%	1.06k ± 0%	~	(all equal)
ParseFungibleToken/Without_memory_metering-2	1.06k ± 0%	1.06k ± 0%	~	(all equal)
ParseInfix-2	66.0 ± 0%	66.0 ± 0%	~	(all equal)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
RuntimeFungibleTokenTransfer-2	4.52k ± 0%	4.52k ± 0%	~	(p=0.592 n=7+7)
RuntimeResourceDictionaryValues-2	37.6k ± 0%	37.6k ± 0%	~	(p=1.000 n=7+7)
Transfer-2	1.00 ± 0%	1.00 ± 0%	~	(all equal)

[codecov]

Codecov Report

Merging #1700 (2e7c3d4) into master (16c5038) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1700   +/-   ##
=======================================
  Coverage   76.64%   76.64%           
=======================================
  Files         292      292           
  Lines       61199    61199           
=======================================
+ Hits        46904    46905    +1     
- Misses      12682    12683    +1     
+ Partials     1613     1611    -2     

Flag	Coverage Δ
unittests	76.64% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/sema/simple_type.go	92.30% <0.00%> (-3.85%)	⬇️
runtime/interpreter/storage.go	69.04% <0.00%> (-1.59%)	⬇️
runtime/sema/type.go	89.02% <0.00%> (+0.07%)	⬆️
runtime/sema/checker.go	90.22% <0.00%> (+0.10%)	⬆️

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