Fix common supertype calculation for optionals

[SupunS]

Closes #1592

Description

The optionals were not properly unwrapped before going into the struct-common-supertype finding path.

Solution:

• Unwrap the optionals before going further
• Re-wrap the same amount of level of optionals, before returning (if not already contain optionals).

With this, supertype of T, T?, T?? will be T??

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• Targeted PR against master branch
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[SupunS]

Moved these two tests to a dedicated test for optionals

[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit f07c18f
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
ContractInterfaceFungibleToken-2	37.1µs ± 2%	40.4µs ± 7%	+8.91%	(p=0.001 n=6+7)
CheckContractInterfaceFungibleTokenConformance-2	123µs ± 4%	131µs ± 2%	+6.92%	(p=0.001 n=7+6)
InterpretRecursionFib-2	2.56ms ± 3%	2.66ms ± 3%	+3.97%	(p=0.008 n=6+7)
QualifiedIdentifierCreation/Three_levels-2	134ns ± 4%	138ns ± 1%	+2.87%	(p=0.038 n=7+6)
RuntimeFungibleTokenTransfer-2	1.09ms ±28%	1.12ms ±26%	~	(p=0.535 n=7+7)
RuntimeResourceDictionaryValues-2	6.14ms ± 7%	6.17ms ± 3%	~	(p=1.000 n=7+7)
Transfer-2	81.1ns ± 6%	82.0ns ± 6%	~	(p=0.805 n=7+7)
ParseDeploy/decode_hex-2	1.12ms ± 4%	1.13ms ± 5%	~	(p=0.620 n=7+7)
ParseInfix-2	8.09µs ± 6%	8.30µs ± 4%	~	(p=0.209 n=7+7)
ParseArray-2	12.5ms ±11%	12.4ms ± 9%	~	(p=1.000 n=7+7)
ParseFungibleToken-2	174µs ± 4%	178µs ± 6%	~	(p=0.731 n=6+7)
QualifiedIdentifierCreation/One_level-2	2.26ns ± 9%	2.34ns ± 0%	~	(p=0.780 n=7+5)
NewInterpreter/new_interpreter-2	1.11µs ± 5%	1.14µs ± 3%	~	(p=0.628 n=7+6)
NewInterpreter/new_sub-interpreter-2	2.13µs ± 5%	2.18µs ± 4%	~	(p=0.165 n=7+7)
ParseDeploy/byte_array-2	19.7ms ± 6%	18.8ms ± 4%	−4.48%	(p=0.038 n=7+7)
	alloc/op		delta
RuntimeFungibleTokenTransfer-2	273kB ± 0%	273kB ± 0%	~	(p=0.435 n=7+7)
RuntimeResourceDictionaryValues-2	2.25MB ± 0%	2.25MB ± 0%	~	(p=0.710 n=7+7)
Transfer-2	48.0B ± 0%	48.0B ± 0%	~	(all equal)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.7kB ± 0%	26.7kB ± 0%	~	(p=0.592 n=7+7)
CheckContractInterfaceFungibleTokenConformance-2	66.3kB ± 0%	66.3kB ± 0%	~	(p=1.000 n=7+7)
InterpretRecursionFib-2	1.14MB ± 0%	1.14MB ± 0%	~	(p=0.923 n=6+7)
NewInterpreter/new_interpreter-2	848B ± 0%	848B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.34kB ± 0%	1.34kB ± 0%	~	(all equal)
	allocs/op		delta
RuntimeFungibleTokenTransfer-2	4.58k ± 0%	4.58k ± 0%	~	(p=0.991 n=7+7)
RuntimeResourceDictionaryValues-2	37.6k ± 0%	37.6k ± 0%	~	(p=1.000 n=5+7)
Transfer-2	1.00 ± 0%	1.00 ± 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)
ContractInterfaceFungibleToken-2	460 ± 0%	460 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
InterpretRecursionFib-2	23.8k ± 0%	23.8k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	13.0 ± 0%	13.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	40.0 ± 0%	40.0 ± 0%	~	(all equal)

[codecov]

Codecov Report

Merging #1594 (85dedf2) into master (f07c18f) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1594      +/-   ##
==========================================
+ Coverage   74.72%   74.73%   +0.01%     
==========================================
  Files         288      288              
  Lines       55305    55340      +35     
==========================================
+ Hits        41324    41359      +35     
  Misses      12487    12487              
  Partials     1494     1494              

Flag	Coverage Δ
unittests	74.73% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
runtime/sema/type_tags.go	94.42% <100.00%> (+0.45%)	⬆️

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[turbolent]

Great fix!