Evaluate if BitArray() can be further optimized using single AddPairwise operation

[kunalspathak]

Evaluate if

runtime/src/libraries/System.Collections/src/System/Collections/BitArray.cs

Lines 190 to 216 in 8511b5b

	{
	// Same logic as SSE2 path, however we lack MoveMask (equivalent) instruction
	// As a workaround, mask out the relevant bit after comparison
	// and combine by ORing all of them together (In this case, adding all of them does the same thing)
	Vector128<byte> lowerVector = AdvSimd.LoadVector128((byte*)ptr + i);
	Vector128<byte> lowerIsFalse = AdvSimd.CompareEqual(lowerVector, zero);
	Vector128<byte> bitsExtracted1 = AdvSimd.And(lowerIsFalse, s_bitMask128);
	bitsExtracted1 = AdvSimd.Arm64.AddPairwise(bitsExtracted1, bitsExtracted1);
	bitsExtracted1 = AdvSimd.Arm64.AddPairwise(bitsExtracted1, bitsExtracted1);
	bitsExtracted1 = AdvSimd.Arm64.AddPairwise(bitsExtracted1, bitsExtracted1);
	Vector128<short> lowerPackedIsFalse = bitsExtracted1.AsInt16();
	Vector128<byte> upperVector = AdvSimd.LoadVector128((byte*)ptr + i + Vector128<byte>.Count);
	Vector128<byte> upperIsFalse = AdvSimd.CompareEqual(upperVector, zero);
	Vector128<byte> bitsExtracted2 = AdvSimd.And(upperIsFalse, s_bitMask128);
	bitsExtracted2 = AdvSimd.Arm64.AddPairwise(bitsExtracted2, bitsExtracted2);
	bitsExtracted2 = AdvSimd.Arm64.AddPairwise(bitsExtracted2, bitsExtracted2);
	bitsExtracted2 = AdvSimd.Arm64.AddPairwise(bitsExtracted2, bitsExtracted2);
	Vector128<short> upperPackedIsFalse = bitsExtracted2.AsInt16();
	int result = AdvSimd.Arm64.ZipLow(lowerPackedIsFalse, upperPackedIsFalse).AsInt32().ToScalar();
	if (!BitConverter.IsLittleEndian)
	{
	result = BinaryPrimitives.ReverseEndianness(result);
	}
	m_array[i / 32u] = ~result;
	}

can be further optimized by doing just 1 AddPairwise with better mask, the way it is done in TryFindFirstMatchedLane.

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[Gnbrkm41]

Might be related: #33749 (comment)

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