Removing recursion in array.fs where it is may be worthwhile

[jackmott]

I went through testing for opportunities to improve performance when recursive versions could be turned into explicit loops. For many cases it was a very small difference - 1% to 2%. If that is deemed worthwhile I can roll those into this PR (would include functions like pick, and find, etc)

compareWith got a 20% performance improvement so seems like an clear win. concat was a very small performance improvement, but I was also able to bring it down from 4 functions to just 2, so it is arguably simpler as well. I could pull this out though if the recursive implementation is preferred.

compareWith

Method	Length	Median	StdDev	Scaled	Gen 0	Gen 1	Gen 2	Bytes Allocated/Op
Old	10	23.7544 ns	0.3000 ns	1.00	-	-	-	0.00
New	10	20.6222 ns	0.2443 ns	0.87	-	-	-	0.00
Old	10000	16,515.5425 ns	137.0188 ns	1.00	-	-	-	7.08
New	10000	13,171.2588 ns	194.4002 ns	0.80	-	-	-	7.09
Old	1000000	1,741,685.5271 ns	46,344.7793 ns	1.00	-	-	2.00	58,857.83
New	1000000	1,430,355.4282 ns	20,364.5100 ns	0.82	-	-	1.00	29,901.96

concat (where length is how many arrays are being concatted, each array being 5 elements)

Method	Length	Median	StdDev	Scaled	Gen 0	Gen 1	Gen 2	Bytes Allocated/Op
Old	10	313.5194 ns	6.8561 ns	1.00	0.02	-	-	96.07
New	10	303.6155 ns	3.8994 ns	0.97	0.02	-	-	92.10
Old	5000	157,129.6265 ns	2,104.6524 ns	1.00	-	-	8.96	41,074.92
New	5000	156,494.2465 ns	4,158.5105 ns	1.00	-	-	9.05	41,470.82
Old	500000	17,492,839.3981 ns	181,163.9916 ns	1.00	75.00	75.00	96.00	5,711,591.54
New	500000	17,198,734.2853 ns	146,830.3554 ns	0.98	81.67	77.59	65.34	4,449,222.19

environment for tests

Host Process Environment Information:
BenchmarkDotNet=v0.9.8.0
OS=Microsoft Windows NT 6.2.9200.0
Processor=Intel(R) Core(TM) i7-4712HQ CPU 2.30GHz, ProcessorCount=8
Frequency=2240908 ticks, Resolution=446.2477 ns, Timer=TSC
CLR=MS.NET 4.0.30319.42000, Arch=64-bit RELEASE [RyuJIT]
GC=Concurrent Workstation
JitModules=clrjit-v4.6.1590.0
Type=SIMDBenchmark Mode=Throughput Platform=X64 Jit=RyuJit GarbageCollection=Concurrent Workstation 

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[KevinRansom]

@jackmott

This is great.

Thank you