[ProfileData] Add getValueArrayForSite (#95335)

Without this patch, a typical traversal over the value data looks
like:

  uint32_t NV = Func.getNumValueDataForSite(VK, S);
std::unique_ptr<InstrProfValueData[]> VD = Func.getValueForSite(VK, S);
  for (uint32_t V = 0; V < NV; V++)
    Do something with VD[V].Value and/or VD[V].Count;

This patch adds getValueArrayForSite, which returns
ArrayRef<InstrProfValueData>, so we can do:

  for (const auto &V : Func.getValueArrayForSite(VK, S))
    Do something with V.Value and/or V.Count;

I'm planning to migrate the existing uses of getValueForSite to
getValueArrayForSite in follow-up patches and remove getValueForSite
and getNumValueDataForSite.