JIT: Do not mark small types RegOptional as part of GT_LONG contained by HWIntrinsic

[saucecontrol]

Fixes #118466

I was unable to get the repro from #118466 to fail when converted to an Xunit test, but this fixes the assert (and codegen) seen in the standalone repro.

Before (when bypassing the assert):

IN0015: 00004E xor      edx, edx
IN0016: 000050 vmovd    xmm0, dword ptr [V00 ebp-0x08]
IN0017: 000055 vpinsrd  xmm0, xmm0, edx, 1
IN0018: 00005B vpbroadcastq xmm0, xmm0

After:

IN0015: 00004E movzx    edx, byte  ptr [V00 ebp-0x08]
IN0016: 000052 xor      ecx, ecx
IN0017: 000054 vmovd    xmm0, edx
IN0018: 000058 vpinsrd  xmm0, xmm0, ecx, 1
IN0019: 00005E vpbroadcastq xmm0, xmm0

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[AndyAyersMS]

@dotnet/jit-contrib FYI

[AndyAyersMS]

Thank you for fixing this.