Fix comments for StorageMap ReadValue and WriteValue

[turbolent]

Description

The comments for the functions for StorageMap.ReadValue and WriteValue were outdated.
Update the comments to the new behaviour.

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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 71986de
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -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
RuntimeFungibleTokenTransfer-2	1.79ms ±29%	1.62ms ±36%	~	(p=0.209 n=7+7)
RuntimeResourceDictionaryValues-2	19.4ms ± 3%	19.4ms ± 6%	~	(p=0.902 n=7+7)
ParseDeploy/byte_array-2	28.9ms ±15%	27.7ms ± 4%	~	(p=0.731 n=7+6)
ParseDeploy/decode_hex-2	1.68ms ± 5%	1.67ms ± 3%	~	(p=0.535 n=7+7)
ParseArray-2	18.2ms ± 4%	17.7ms ± 3%	~	(p=0.051 n=6+7)
ParseInfix-2	11.9µs ± 3%	12.1µs ± 6%	~	(p=0.628 n=6+7)
ParseFungibleToken-2	274µs ± 2%	283µs ±10%	~	(p=0.456 n=7+7)
QualifiedIdentifierCreation/One_level-2	3.99ns ± 5%	3.89ns ± 3%	~	(p=0.104 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	199ns ± 3%	194ns ± 3%	~	(p=0.073 n=7+6)
ContractInterfaceFungibleToken-2	61.1µs ±13%	58.5µs ± 3%	~	(p=0.181 n=7+6)
CheckContractInterfaceFungibleTokenConformance-2	209µs ± 6%	210µs ± 2%	~	(p=0.366 n=7+6)
NewInterpreter/new_interpreter-2	1.53µs ± 3%	1.53µs ± 4%	~	(p=1.000 n=6+7)
NewInterpreter/new_sub-interpreter-2	2.97µs ± 2%	2.99µs ± 4%	~	(p=1.000 n=6+6)
InterpretRecursionFib-2	3.30ms ± 2%	3.30ms ± 2%	~	(p=0.818 n=6+6)
	alloc/op		delta
RuntimeFungibleTokenTransfer-2	282kB ± 0%	282kB ± 0%	~	(p=0.643 n=7+7)
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	~	(p=0.420 n=6+6)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.6kB ± 0%	26.6kB ± 0%	~	(p=0.385 n=7+6)
CheckContractInterfaceFungibleTokenConformance-2	66.2kB ± 0%	66.2kB ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	768B ± 0%	768B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.24kB ± 0%	1.24kB ± 0%	~	(all equal)
InterpretRecursionFib-2	1.24MB ± 0%	1.24MB ± 0%	~	(p=0.714 n=7+7)
	allocs/op		delta
RuntimeFungibleTokenTransfer-2	4.54k ± 0%	4.54k ± 0%	~	(p=0.804 n=7+7)
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.906 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	458 ± 0%	458 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	12.0 ± 0%	12.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	38.0 ± 0%	38.0 ± 0%	~	(all equal)
InterpretRecursionFib-2	25.0k ± 0%	25.0k ± 0%	~	(all equal)