Improve Performance of SVE microbenchmarks

[ylpoonlg]

This PR includes various improvements to the existing routines in SVE microbenchmark:

• Improve Scalar performance by using fixed pointers for array access. This makes the comparison fairer against vector counterparts.
• Rework StrIndexOf SVE implementations to improve performance. Also makes the Neon implementation more similar to GetIndexOfFirstNonAsciiChar in the C# SDK.
• Add a SveTail version to Partition to avoid unnecessary conversions between predicates and vectors in the codegen.

Benchmark results

(Run on Nvidia Grace)

StrIndexOf:

Method	Size	Mean (Before)	Mean (After)	Speedup
Scalar	19	4.7269 ns	2.5919 ns	0.548x
Vector128IndexOf	19	3.7376 ns	0.3231 ns	0.086x
SveIndexOf	19	3.7094 ns	1.2280 ns	0.331x
SveTail	19	3.6244 ns	0.6806 ns	0.188x
Scalar	127	33.7784 ns	19.5391 ns	0.578x
Vector128IndexOf	127	24.9000 ns	2.0279 ns	0.081x
SveIndexOf	127	24.9709 ns	9.8849 ns	0.396x
SveTail	127	23.3407 ns	5.0614 ns	0.217x
Scalar	527	136.6931 ns	83.2942 ns	0.609x
Vector128IndexOf	527	31.3376 ns	12.3589 ns	0.394x
SveIndexOf	527	63.5482 ns	44.2022 ns	0.696x
SveTail	527	48.8708 ns	25.6798 ns	0.525x
Scalar	10015	2,656.9679 ns	1,559.0106 ns	0.587x
Vector128IndexOf	10015	390.8402 ns	288.6259 ns	0.738x
SveIndexOf	10015	964.7415 ns	903.0951 ns	0.936x
SveTail	10015	700.3612 ns	544.0103 ns	0.777x

Partition:

Method	Size	Mean	Error	StdDev	Median	Min	Max	Allocated
Scalar	15	6.197 ns	0.1209 ns	0.0944 ns	6.170 ns	6.160 ns	6.496 ns	-
SvePartition	15	9.900 ns	0.0062 ns	0.0055 ns	9.901 ns	9.887 ns	9.907 ns	-
SveTail	15	4.456 ns	0.0056 ns	0.0052 ns	4.455 ns	4.448 ns	4.466 ns	-
Scalar	127	44.955 ns	4.5136 ns	5.0168 ns	41.902 ns	41.839 ns	55.372 ns	-
SvePartition	127	87.033 ns	0.0430 ns	0.0381 ns	87.027 ns	86.974 ns	87.101 ns	-
SveTail	127	56.420 ns	0.4204 ns	0.3932 ns	56.192 ns	56.121 ns	57.086 ns	-
Scalar	527	229.889 ns	39.2392 ns	45.1879 ns	243.624 ns	179.879 ns	302.881 ns	-
SvePartition	527	367.581 ns	0.2514 ns	0.2099 ns	367.634 ns	367.056 ns	367.881 ns	-
SveTail	527	249.846 ns	0.5340 ns	0.4995 ns	249.587 ns	249.369 ns	250.973 ns	-
Scalar	10015	3,559.428 ns	1.3667 ns	1.2115 ns	3,558.985 ns	3,558.258 ns	3,561.871 ns	-
SvePartition	10015	6,525.739 ns	10.5519 ns	9.8703 ns	6,526.970 ns	6,506.622 ns	6,541.882 ns	-
SveTail	10015	5,270.654 ns	3.6844 ns	3.0766 ns	5,270.898 ns	5,264.652 ns	5,277.305 ns	-

[ylpoonlg]

@dotnet/arm64-contrib @a74nh

[SwapnilGaikwad]

Hi @LoopedBard3, could you take a look at this PR, please?