Add equality override for KeyValuePairComparer

[johnthcall]

I noticed that SortedDictionary copying was allocation more memory than iterating the initial dictionary and adding items one at a time. I realized that the optimization done as part of #45659 was not completely successful and we need to override Equals for KeyValuePairComparer so that SortedSets HasEqualComparer will pass to allow efficient deep copy.

dotnet/performance@main...johnthcall:johncall/SortedSetDeepCopy

Method	Toolchain	N	Mean	Error	StdDev	Ratio	Allocated
SortedDictionaryCopy	main	1	233.25 ns	14.931 ns	17.195 ns	1.00	392 B
SortedDictionaryCopy	pr	1	179.63 ns	4.817 ns	5.547 ns	0.77	344 B
SortedDictionaryCopy	main	10	1,353.38 ns	55.142 ns	63.501 ns	1.00	1,136 B
SortedDictionaryCopy	pr	10	600.19 ns	30.233 ns	34.817 ns	0.44	944 B
SortedDictionaryCopy	main	100	16,490.14 ns	785.823 ns	904.955 ns	1.00	7,664 B
SortedDictionaryCopy	pr	100	4,805.14 ns	91.329 ns	89.697 ns	0.29	6,080 B
SortedDictionaryCopy	main	1000	212,509.48 ns	10,768.851 ns	11,969.549 ns	1.00	72,512 B
SortedDictionaryCopy	pr	1000	48,069.80 ns	1,324.823 ns	1,525.668 ns	0.23	56,576 B

[eiriktsarpalis]

Thanks!

[drieseng]

@johnthcall Did you create a PR for the benchmark?

[johnthcall]

@drieseng I did not create a PR for the benchmark as I was just sharing the branch so that the reviewer could verify the validity of the benchmark results. Should a PR be made to cover these scenarios?

[eiriktsarpalis]

Should a PR be made to cover these scenarios?

Adding the benchmark to dotnet/performance would be nice to have.