Don't have getVectorTByteLength() return 0 for the time being

[tannergooding]

This resolves#87515, resolves#87511, resolves#87388

The proper fix for this is tracked by #87502, but for the time being we'll continue matching what we did in .NET Core 2.0 through .NET 7

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Issue Details

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This resolves #87515, resolves #87511, resolves #87388

The proper fix for this is tracked by #87502, but for the time being we'll continue matching what we did in .NET Core 2.0 through .NET 7

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

[tannergooding]

CC. @dotnet/jit-contrib. Small fix for 3 of the DOTNET_EnableHWIntrinsic issues that were showing up for Arm64.

It just reverts us back to the behavior we had in .NET 7 (and prior releases) where we report the Vector size to be the 16-byte register even if HWIntrinsics are disabled.

Allowing it to report 0 will require more work and ensuring that any required ABI related handling remains correct in the face of that.