Fix field initialization: nested intersection should not override outer set

[turbolent]

Closes #1523

Description

If-statement branches are checked using Checker.checkConditionalBranches.
It temporarily creates a new child member set, checks each branch with the temporary member set (using Checker.checkWithInitializedMembers, then "merges" the result by building an intersection (a field is considered initialized if it was initialized in both branches).

The existing implementation was overwriting the outer if-statements member set.

Instead, mutate the current member set in-place when computing the intersection.

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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

[codecov-commenter]

Codecov Report

Merging #1524 (86f8b58) into master (5238cce) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1524   +/-   ##
=======================================
  Coverage   74.68%   74.68%           
=======================================
  Files         289      289           
  Lines       55607    55602    -5     
=======================================
  Hits        41528    41528           
+ Misses      12584    12580    -4     
+ Partials     1495     1494    -1     

Flag	Coverage Δ
unittests	74.68% <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/check_conditional.go	93.66% <100.00%> (ø)
runtime/sema/member_set.go	93.75% <100.00%> (-0.59%)	⬇️
runtime/sema/ordered_map_member_struct.go	49.29% <0.00%> (+7.04%)	⬆️

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[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit 668062c
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	1.55ms ±24%	1.54ms ±24%	~	(p=0.805 n=7+7)
RuntimeResourceDictionaryValues-2	17.0ms ± 4%	16.9ms ± 3%	~	(p=1.000 n=7+7)
ParseArray-2	18.4ms ± 2%	18.6ms ± 6%	~	(p=0.628 n=6+7)
ParseInfix-2	10.0µs ± 2%	10.2µs ± 3%	~	(p=0.209 n=7+7)
ParseDeploy/byte_array-2	30.8ms ± 9%	31.2ms ± 6%	~	(p=0.902 n=7+7)
ParseDeploy/decode_hex-2	1.43ms ± 1%	1.43ms ± 1%	~	(p=0.445 n=6+7)
ParseFungibleToken-2	224µs ± 4%	226µs ± 3%	~	(p=0.535 n=7+7)
QualifiedIdentifierCreation/One_level-2	2.81ns ± 0%	2.80ns ± 1%	~	(p=0.383 n=6+7)
CheckContractInterfaceFungibleTokenConformance-2	161µs ± 1%	161µs ± 3%	~	(p=0.620 n=7+7)
ContractInterfaceFungibleToken-2	49.1µs ± 4%	48.8µs ± 3%	~	(p=0.620 n=7+7)
InterpretRecursionFib-2	3.26ms ± 5%	3.33ms ± 3%	~	(p=0.128 n=7+7)
NewInterpreter/new_interpreter-2	1.38µs ± 4%	1.40µs ± 3%	~	(p=0.383 n=7+7)
NewInterpreter/new_sub-interpreter-2	2.74µs ± 4%	2.73µs ± 1%	~	(p=0.684 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	171ns ± 2%	168ns ± 2%	−1.87%	(p=0.011 n=7+7)
	alloc/op		delta
RuntimeFungibleTokenTransfer-2	273kB ± 0%	273kB ± 0%	~	(p=0.165 n=7+7)
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	~	(p=0.477 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)
CheckContractInterfaceFungibleTokenConformance-2	66.2kB ± 0%	66.2kB ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.6kB ± 0%	26.6kB ± 0%	~	(p=0.592 n=7+7)
InterpretRecursionFib-2	1.26MB ± 0%	1.26MB ± 0%	~	(all equal)
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	4.54k ± 0%	4.54k ± 0%	~	(p=1.000 n=7+7)
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.272 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)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	458 ± 0%	458 ± 0%	~	(all equal)
InterpretRecursionFib-2	26.2k ± 0%	26.2k ± 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)