Ensure that `EnableHWIntrinsic=0` can have `getMaxVectorByteLength` return `0`

[tannergooding]

#87420 reverted the behavior of getMaxVectorByteLength back to returning 16 as the minimum size, even when EnableHWIntrinsic=0

This matches the behavior we've had for many releases. Longer term, we need to ensure that the various ABI, P/Invoke, and other handling is well behaved when EnableHWIntrinsic=0 and the reported maximum vector size the JIT can use is 0.

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Issue Details

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#87420 reverted the behavior of getMaxVectorByteLength back to returning 16 as the minimum size, even when EnableHWIntrinsic=0

This matches the behavior we've had for many releases. Longer term, we need to ensure that the various ABI, P/Invoke, and other handling is well behaved when EnableHWIntrinsic=0 and the reported maximum vector size the JIT can use is 0.

Author:	tannergooding
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	Future